Is there such thing as "luck" in chess?

divine providence:  God has authored it.

I was just trolling you in this specific case man, was not meant to be taken seriously. 

But in an effort to get back on track, I don't think the second half of your definition is reasonable. I mention it in my reply to Optimissed, but I haven't found anybody other than yourself who includes or insinuates anything like the whole second half of your definition ("or not being able to increase ones chance of success with practice or knowledge") in theirs. By including it, you are almost defining the word as the conclusion of your argument, similar to how I sarcastically gave my faux definition.

My stance has always been that chess and other games, sports, and activities are largely skills-based, but that doesn't absolve them of having elements of luck within them. For reference, my actual definition of luck is something akin to: "success or failure apparently brought by chance rather than through one's own actions". I think chess is encapsulated in this definition because in any position, one cannot attribute move selection exclusively to skill any more than they can attribute the selection of a correct door in Monty Hall's old show to skill. We can only get a reference to a person's relative skill through prior information we have about them and through multiple trials.

So as an example, I take an intentionally extreme/limiting situation to help think about it. In any given position, someone who doesn't even know how pieces move can make the "correct" move while a grandmaster can make an "incorrect" one. This fits the definition of luck I used since the outcome of the move is not representative of a fundamental difference in skill. It is based on the action of moving the piece, but only in the same way that the outcome of a dice roll is based on the action of the person rolling it.

One might say that that is not really playing chess, but if you do so, you are essentially back filling a person's intentions and categorizing their skillfulness or lack thereof based on the outcome of the move which has already occurred. To me, that is flawed thinking both because it is unfalsifiable, and because it is somewhat circular reasoning ("Q: What lead to the good move? A: The person's training/intuition/etc. Q: What evidence supports this? A: It was a good move")

randomly selecting moves means you're not playing chess.    🙂

Here, we agree. 

I have done that. I have been in situations where I had absolutely no idea what to do. None. The clock is ticking. I have to move. 

So I didn't make a move that would be considered an obvious mistake, but there have been times where I can't decide between 6 or 8 seemingly equal moves. So I just guess. Intuition, hunch, hope, etc. I don't know if that's luck, but it's certainly random. 

guessing moves is not playing chess:

poor clock management is a skill issue, anyways.

A lot of people ask me why I close.

But for example, if I were trying to hide my identity, why would I choose the same name?

Closing your account does not remove your posts.

This is one of a few really annoying topics that go on and on long after the best answer was  already given.

My version of the answer (probably buried in here somewhere on one of my past accounts) is that the rules of chess describe a game with no luck, but when humans play it there is a non-zero amount of luck.

There have been multiple examples given. 

That's probably true. But I'll bet even the best players in the world, when given three or four seemingly identical choices have to decide on a move, using nothing more than randomness. Not luck maybe, but best guess or intuition. 

Regarding luck, one fun example is the, at times inverse, relationship between knowledge and performance captured by the saying "a little knowledge is a dangerous thing."

It's easy to imagine sacrifices (or other situations) where we might say "only a beginner or a GM would play such a move" and it works for bad moves too. For example knowing enough to feel threatened and defend, but not knowing enough to realize the threat can be ignored.

Depending on our energy level during the game, we might gain more or less knowledge through calculation. Where you stop, and whether the knowledge gained will be useful, has an element of luck.

Also, in many positions a human player is not planning for discrete sequences, they're using heuristics to maximize the probability their move is good. A simple example is mobility. The more squares a piece can move to, the higher probability it will be able to move to a useful square in the future. This means future positions sometimes arise without either player explicitly planning to reach them. Whether each player's knowledge and heuristics will be useful in that unplanned-on position has an element of luck.

Even engines are making their best guess. I remember Rybka programmers saying that they tested changes by having an engine play many games. In some positions the changes caused the engine to play worse, but if the overall performance was higher, then the changes were kept.

One of the early posts in this topic summed it up well saying this is why we play matches, not single games. In probability this concept is known as the law of large numbers. The more times you repeat a random process, the more likely the cumulative results tend towards the expected value. In other words matches with more games have a greater chance of determining the better player.

     Yes, but neither are the deliberately chosen moves. I take a lot of time and many typos to send messages on my phone, an unfortunate "Fringe benefit"of old age, deteriorating agility and poor eyesight. Does this mean that should I make an unintended move I should have had the "skill" to have  been born later?

     Exactly. As you say, luck (or chance, serendipity, fate, divine intervention, randomness--whatever you choose to call it) can affect ANY game. Even chess.

they are using an internally-trained system of weights & measures to assess the relevance of various factors in any given position, to determine the viability of each candidate move as contrasted with the others, similar to A0's neural network.

chess as an 'art of logical thinking' is essentially infinite to our limited minds, but the more skilled player, who is better at visualizing, calculating & assessing upcoming lines of play is superior...

you can't outrun a bear, but you can outrun your friend that you're hiking with:   😆

were you lucky that he got eaten?

no, you took track in high school.

Certainly, luck exists - You're playing your opponent while he's waiting for the bus  ... and the bus runs over him.    However, I wouldn't depend on it. 

You get food poisoning, the night before your big tournament game.

The next day, you try to play through the foggy head, through the stomach cramps, through the cold sweats and shakiness. Not showing up isn't an option - a no-show is an automatic forfeit.

But it's hard to focus. Every thought feels like a lead anchor, dragging through your mind. Your vision is blurry and you feel like you're going to fall over and pass out.

You place your bishop on the wrong color diagonal, because it's hard to mentally keep track of the squares, and your opponent calls the arbiter. The arbiter frowns at you, resets the position, and takes time off your clock. You should be winning - your opponent doesn't even know the proper lines. He keeps hanging pieces, but you keep missing them - only realizing it after the fact.

You eventually stumble into a completely lost position, missing a beginner-level tactic that you normally would never miss. Your performance level is several hundred points below your norm.

You resign in dismay, feeling ashamed of your performance, and regretting the beef strips that you ate the night before. Your opponent is visibly elated over beating you. He tells you that he's never beaten someone of your rating, before.

You mumble a grudging congratulations, then rush to the bathroom for another round of vomiting.

Bad luck for you - good luck for your opponent.

bad ordering... try well done next time:

your skill level was exactly as expected, considering the tournament performance circumstances;

bummer for you, but life isn't fair sometimes.

Perhaps.

Okay, I got one. You are black, it is your move.

You intend to play ...QxQ, followed by ...Bxc5.

You pick up the queen, you reach over to your opponent's side of the board ...

But as you're setting your piece down to exchange queens, you suddenly sneeze.

When you look at the board a split-second later, you have released your queen ... on the wrong square.

In a panic, you stop the clock and call the arbiter to explain your circumstances.

The arbiter is sympathetic, but informs you that a deliberate move can only be exempt, in such a case, if it were clearly the result of "accidental touching". He tells you that the queen cannot be moved from d8 to d2 as a result of "accidental touching".

The arbiter restarts the clock and allows your opponent to play the next move:

Bad luck for you, good luck for your opponent.

In online chess yes, if opponent is winning and opponents internet connection just get lost somewhere........

In real table chess no luck its all about your brain and practice.

Luck exists everywhere. It might be a bit difficult to imagine how luck would play a part in chess as opposed to other sports where the form in which luck -good or otherwise- presents itself is easier to think of. For example, in Cricket, luck might make a the ball hit just the sweet spot on the bat leading to the batsman scoring a 6. (Pardon the Cricket terminology, 6 is just a high score, basically). In Chess, where you are moving a piece one square ahead, luck doesn't have much to do with that does it? The piece goes where you want it to go and rules define the significance of that move. However luck can present itself in other forms then. For example, one player may become sick leading them to forfeit and giving the other an easy victory. One player may have had a tremendous day before the match which can lead them to have a positive mindset for the duration of the game, causing them to perform flawlessly. The list can literally go on forever, luck exists everywhere.