“I like the moment when I break a man's ego” - Fischer
"The winner of the game is the player who makes the next-to-last mistake." - Tartakover
The psycholgy of losing

A couple of extra reasons why players hate to lose.
1. Team or national pride is at stake, such as in the Olympiads.
2. Some players advocate a way of chess thinking (Steinitz and Nimzowitsch, for example), or an opening system. So their wins can be used to back up their arguments, but detractors will point to their losses to imply their chess thinking is unsound. So the stakes are higher than mere personal reputation.
Some people will say it is reasonable for a player to make an excuse for a loss by saying he was jetlagged, or had a cold, etc. Perhaps.
But here's the thing: when a player wins, he takes all the credit for himself. You will never hear a player say, "I won that game because my opponent was jetlagged, or was going through a stressful divorce, or had food poisoning" and so on.
No, the win is owed to his natural chess genius flowering: "I am Capablanca come again! Alekhine bows to me!" ☺
It is only when people lose that they start casting around for excuses and scapegoats. This is the natural bias of the ego.

When I win. There’s a quick dopamine response and positive reinforcement to my game, then it’s on to the next.
Definitely more pain in a loss than pleasure from winning.

//Definitely more pain in a loss than pleasure from winning.//
Yes, that's natural. Everyone feels that way. But as you say, that pain provides the impetus to improve.
I see it this way:
1. Try
2. Fail
3. Review
4. Improve
5. Try again.
This is a natural feedback cycle. It is not a circle but a spiral because it goes upwards to higher perfomance.

Whenever I lose a game where I was completely winning, I just can't bring myself to thoroughly analyze it. Like it somehow pains me to have to look at the many ways I threw away my big advantage even though no one else is watching. Yet, because of this habit I keep making the same mistakes again and again and again. Truly one of the biggest roadblocks in my chess improvement that I'm trying to overcome at the moment.

//Whenever I lose a game where I was completely winning, I just can't bring myself to thoroughly analyze it. Like it somehow pains me to have to look at the many ways I threw away my big advantage //
Yes, it's painful to go over our mistakes and blunders. But that's exactly where the improvments are to be had. We have to go directly to the weak points.
A medical analogy: a person has a wound on his arm. He doesn't clean it, but just hides it with a dirty cloth, hoping it will clear up by itself. But left in that state, the wound becomes infected and much more serious.
In the same way, we have to expose our mistakes and blunders to the iodine of informed review. Otherwise, how can we improve?
Botvinnik is a model in this respect. After playing a game, he tore it to analytical shreds - even the ones he had won! He never rested on his laurels. Even such a great player as that was relentless in his efforts to improve. So what are us lesser mortals doing?

//Whenever I lose a game where I was completely winning, I just can't bring myself to thoroughly analyze it. Like it somehow pains me to have to look at the many ways I threw away my big advantage //
Yes, it's painful to go over our mistakes and blunders. But that's exactly where the improvments are to be had. We have to go directly to the weak points.
A medical analogy: a person has a wound on his arm. He doesn't clean it, but just hides it with a dirty cloth, hoping it will clear up by itself. But left in that state, the wound becomes infected and much more serious.
In the same way, we have to expose our mistakes and blunders to the iodine of informed review. Otherwise, how can we improve?
Botvinnik is a model in this respect. After playing a game, he tore it to analytical shreds - even the ones he had won! He never rested on his laurels. Even such a great player as that was relentless in his efforts to improve. So what are us lesser mortals doing?
Well said fellow chess comrade

I agree with the OP the reality is hard to swallow when I lose - I was outplayed - my opponent was better than me in this - the ego really doesn't like this. As @lotus960 says it's only by accepting the reality in an adult way there is any chance of real improvement.
The fact that in chess there is nothing to hide behind - no 'luck' no chance gamble etc. is what makes it so attractive - and so painful. It's a chance to truly measure our ability against another's on a level playing field. It's humbling for me (nearly 50) to lose against a nine yr old player and admit it's because they were simply better, but it gives a chance for me to develop a little perspective and a sense of humour. I may not be improving in chess but I'm improving as a human who is less negatively influenced by my instant ego response.

@Open Squirrel
Well said. And thanks for adding the point about it being extra difficult to lose to a kid. With all the prodigies around these days, it can happen.
It's important to have a sense of self-worth that is not dependent on chess. That way, we can put a loss into perspective.
Thinking about bad losers, David Bronstein comes to mind. He never got over his loss to Botvinnik in their WCC match, and even years afterwards he would buttonhole people about it. His fellow Soviet GMs learned to avoid him.
Another was Korchnoi. A world-class player, and also a world-class excuse-maker. The 1978 match in the Philippines descended into farce: X-rays of seats, complaints about a parapsychologist supposedly beaming thoughts at Korchnoi, yoghurt disputes, Indian cult members turning up, etc. A real circus.
This is from Korchnoi's written complaint to Chief Arbiter Schmid:
//It is clear that a cunningly arranged
distribution of edible items to one player during the game, emanating from one delegation or the other, could convey a kind of code message.
Thus a yogurt after move 20 could signify "we instruct you to offer a draw"; or a sliced mango could mean "we order you to decline a draw". A dish of marinated quails' eggs could mean "play Ng4 at once" and so on. The possibilities are limitless.//
Clearly, at this point we have descended into paranoia. 😂

@Solmyr1234
//Cheating is the right way to go.//
That is the dark side of the Force, young Skywalker. Don't go there. ☺

@Ginarook
Hello, thanks for your contribution.
I take your point, but I'm afraid I have to disagree with you. What you write is a combination of two points I made in my OP: 1. Trying to win the game in the post-mortem, and 2. Complaining about time controls.
1. Post-mortem fallacy: "I was winning until ... I was not winning." Yeah, that's what we call a loss. ☺
You yourself say you often blunder at the end and lose that way. Well, your opponent didn't blunder as often and so won the game because they played better moves (or put another way, less bad moves. It's the same thing).
2. As for time controls, whether a player is positional or tactical in style, they still get the same amount of time, and how a player uses that is their responsibility. When you lose on time, your opponent has managed their time better, and so again deserves to win.
I'm not criticising you for what you wrote, because it's universally hard to accept defeat. The human mind is very ingenious, and we all wriggle and squirm to avoid facing the fact that we have not succeeded at something.

We seem to be emphasising slightly different aspects of the issue.
In my OP, I focused on the moves and the final position, because I was more interested in comparing the players' different understandings of chess.
I did mention time controls, but not so much. You on the other hand are putting more emphasis on the time factor.
In the round, I think we both accept that we have to take responsibility for our losses, whether looked at from the point of view of moves or time. Let's agree on that. ☺

@Ginarook
// am disappointed you would put that last sentence, if I lose, I lose and that is my responsibility, whatever the reason.//
Don't be disappointed. You make me feel bad.
And if you look at that last sentence, you will see that I used the word "we", including myself, because it's a univeral tendency and I'm not exempt from it.
Reading about Napoleon recently, I discovered that he played chess and other board games. He hated to lose, so he would often cheat.
This made me think about the psychology of losing. To win is a kind of victory for the ego and a defeat is a blow to it, so players try everything they can to avoid defeat. Napoleon returned his winnings after games in which he cheated, showing that ego was the root motive of his cheating, not monetary gain. As emperor, he was hardly short of money.
There is nothing wrong with a fighting spirit of course, and it is even necessary in chess. But there are many ways a player tries to avoid the fact that he has lost. Why is this so common? I would say the following features of chess make a loss a particularly hard blow.
1. Unlike card and dice games, there is no element of chance. It is a game of knowlege and skill.
2. It is a game of perfect information, with nothing hidden from view.
3. It is difficult to cheat in chess. Although there can be gamesmanship, there aren't any hustlers like card sharpers and dice manipulators. Nor are there secret collusions between players like in Bridge, although there can be agreements to draw in a tournament. (I omit here cheating using a chess engine, which is another topic. )
3. It is not a team effort, so there is no one else to blame like in football, basketball etc.
4. Personal rivalries and jealousies develop between players, making their games grudge matches.
So there are few *rational* reasons to avoid facing up to a defeat. Hence the need to invent a few irrational or specious reasons, based on denial or displacement. Lasker famously quipped that he had never beaten a well man. Here are a few similar rationalisations:
1. Enviromental issues: it's too hot/cold, too early/late, too noisy/quiet etc.
2. Health issues: a cold, the flu, too much/not enough sleep, too full/hungry, jetlagged, hangover after boozing the night before, etc.
3. Trying to win the game in the post-mortem. "If you'd gone here and I'd gone there, I'd have won the game!" Reply: "Yes, but I didn't go here, and you didn't go there, so you lost!"
4. Complaining about time controls, as if these were different for our opponent, or our thinking time was not in our control, or the clocks were somehow biased against us.
To me, the only reasonable and rational response to a defeat is to say this: I lost because my opponent played better moves than I did.
It's really as simple as that. Everything else is just ego obfuscation, displacement and denial. It is also good sportsmanship to accept that our opponent played better and deserved to win.
And here's an important reason why we should accept that rational response: it directs our energies to improving our game. As long as we are in denial and making excuses (external locus of control), we are not psychologically ready to do the work necessary to make improvements in our game (internal locus of control.)
Please add any thoughts or observations you have about the psychology of losing.