Change My View: mastering one opening is better than learning a dozen.

Definitely true for newer players and even for many years this could remain to be true. I'm not sure if there are many less experienced players that learn a lot of openings, except by accident as they are experimenting until they find an opening they love. The only exception for a relatively inexperienced player is if you are attending tournaments and there are enough similarly skilled opponents in attendance, in this case diversifying your opening reppetoire could be worth it to improve your results, as opponents would study against your openings, and so you have the element of surprise.
However even then for long-term improvement I could see an argument for continuing to master your chosen openings until 2000+ or so FIDE when you start to become in contention for titles, as even if your opponent prepares against you in your favourite lines you should still have an advantage by virtue of familiarity of the structure of the position stemming from your favourite opening.
I think the only advantage to learning multiple openings for newer players or even for intermediate and advanced players that don't attend tournaments is if you play a lot against the same few people, for example if you have some chess friends/rivals. In this case it would keep things fresh and you would surprise eachother with new openings, it would be a lot of fun and educational for everybody.
By the time you are a serious competitor in over the board tournaments then you absolutely have to learn multiple openings because your opponents will prepare against rarer moves in your chosen variation, and especially the best lines and the lines you favour in general. In this case competitive players have to prepare solid challenging lines in an opening that an opponent might not expect, or prepare rare and unusual lines in openings that you favour.

I think it is a good idea to change openings every two years or so, to gradually build up broader knowledge and experience. For the first couple of years, one opening for white and one opening for black is a good idea, although your opponents will force you to play different openings from time to time.

Oli, this threads title is misleading, it should be called, "Why I decided to concentrate on learning the Hippo", rather than "blah,blah,blah CMV"

What I would suggest is to learn a dozen openings and of the ones you liked the most, master one. When I first started to take chess seriously, I thought I was a defensive opening player. But then, I tried Kings Gambit, and fell in love with it's aggressive style. But that doesn't mean I'm an aggressive opening player now, coz I'm testing with Vienna Game now. Your "perfect" opening might be lurking out somewhere and you never know.

op is advocating system openings, right?
you cant possibly do what op is doing with a normal repertoire

Olivia, you are onto something. Here's a similar thread from a few years back that makes the same assertation. Enjoy.
https://www.chess.com/forum/view/general/opening-theory-and-vegetarianism-are-both-overated
**P.S. the Hippo is a "universal opening. You can play it with both colors. It saves you from an immense amount of (opening-theory-study time),
Yes, indeed. Ha!

You raise some really good points. I definitely agree that solely focusing on one opening has risks, especially if your opponent deviates from "the script" early on. Then you're forced to figure things out on the fly instead of relying on your preparation.
My success with the Hippo is probably amplified by the fact that it's not a super common opening at my level. So opponents often don't have as much experience playing against it. You're absolutely right that could become a problem as I advance to higher ratings and face opponents who are better prepared.
I should clarify - I'm not suggesting players at higher levels only learn one opening in depth. That would likely be too limiting. But for me as a relative beginner, it has been an effective way to rapidly improve my understanding of key opening principles, plans, tactics, etc.
Your point about considering potential black responses is well taken. I have focused mostly on the "main lines" against the Hippo, so deviations throw me off. Expanding to at least learn the ideas of common black openings would make sense.

Experimenting with openings and finding ones you are most comfortable with is definitely a good idea. For e.g. I experimented with e4 openings as whites and found that I often struggled to adapt to tactical positions, when I switched to c4 - English opening I found it far easier to navigate through the middlegame due to the positions being less sharp in general (usually), but mainly due to me having more ideas and more moves which then allow me to analyze and pick the best one according to my strategy in the position

yeah until your opponent plays a different first move
have fun playing your sveshnikov sicilian against 1. d4
You should get a grip of various different openings against various different responses, and then practice the one you most commonly face

I advocate the opposite approach to the OP.
Study and play the first few moves of many openings, in order to get a broad overview and to become versatile and adaptable in working with many different types of position.
Will you be playing Caruana any time soon? No, I didn't think so. So in-depth preparation is not needed.

I finally looked up the Hippo Opening. I had no idea what the Hippo entailed, however, upon seeing the moves and whites likely position I realized I see this opening a lot! My impression is that my opponents mostly play passively and turtle-up, or wait to see how I will respond, then attempt to counterpunch. The game usually is just a short brawl in the center, then a quick transition to an endgame. I find I do well vs the Hippo, but it's a strangely frustrating experience as white, maybe because its just some drunken bloodletting in the center where I'm not even sure who's winning, until I see it's me and a won endgame...or...it's not me, game over.
Hey everyone! I wanted to talk about a recent chess experiment of mine - diving headfirst into deeply learning a single opening. Or—a position, as some would say.
For the last few months, I've been absolutely obsessed with the Hippopotamus Defense (aka "The Hippo"). I know, it sounds like a silly name, but don't let that fool you. This unconventional opening has been working wonders for me!
Now you might be wondering - why limit yourself to one opening? Wouldn't it be better to study a variety of openings to keep your opponents on their toes? I thought so too at first. But focusing intensively on just the Hippo has improved my chess way more than trying to half-learn ten different openings.
Here's why it works: when I face opponents who haven't prepared for the Hippo's unique style of play, I can steer the game exactly how I want. I know the plans, themes, and ideas so deeply that I hardly have to think. Meanwhile, my opponents are often scrambling to come up with a response. That advantage leads me to score a lot of wins when I am playing seriously.
Trying to learn too many openings can backfire. Sure, you get some variation, but at the cost of never fully grasping any one opening. I found myself struggling to remember all the lines and easy to make silly mistakes right out of the opening that botched my position. No bueno!
Sticking with the Hippo has allowed me to really monitor my progress and improve. My opening play has gotten so much tighter and deliberate lately. I'm absolutely crushing it in the quicker formats like blitz and bullet
. Of course, I may branch out eventually - but becoming a master of one opening first has been a game-changing strategy for me. Maybe this applies to others too?