Level jump at 900 ELO

I'll tell you exactly. Until master level especially even more on lower scale openings aren't important but opening principles. When I were 900, I've selected system (they are antidote for any black's try), namely, London system. Oponents until 1000 will be lost. Have played just that until 1000. Above 1000 opponents will know how to handle that. Then, think just about strategy which leads to tactics. Without strategy, tactical situations will rarely rise. Same as with white stick just to one defense and untill 1000 concetrate just on tactics...

The slightest thing stuck in your head will distract you and bring you down a notch.  Do your best to not think about ratings or who you're playing, or whatever.  You'll have days when a person way lower rated will crush you, and other days where you'll just mop the floor with a person higher rated than you are.  Don't read too much into either one.  Accept that the lower rated person had a good day, and understand that the higher rated player may have caught you on a good day.  Might have been you played bad vs the lower rated player, and the same for your higher rated player, again, don't read too much into it.  Try to learn from every game and be honest with yourself about what you are not doing well and work on that.  Improvement takes time, enjoy the ride. 

Keep in mind, playing a bad position is difficult, playing a good position is often easy.  One mistake often decides a game and it snowballs once the game takes a turn.  It's hard to un-do a mistake without some help from your opponent making one of their own.  Small errors matter, so study your games to find the ones you make and try to avoid them in the future.  That sounds elementary, but look at your game review graphs for a while and it'll seem more profound as time goes on. 

Unless the lower rated player is Hans and the higher rated player getting crushed is Magnus. Amiright or amiright?

Lmao!  Pretty good! 

Ok, engines aside, it takes very little to distract a person from 100% concentration and playing their best.  Not rested, didn't eat, didn't sleep well, stressed with other things, your chess game is diminished.  I don't know how much such things affect other people, but for me it's a big deal.  Quantifiable for sure. 100s of points.  I firmly believe that kids are advantaged at chess largely due to not having to be bothered with the stresses of daily life and keeping a roof over their heads.  Every little bit helps.  And distractions are bad. 

We will see in a few days if you are or not.  I suspect Hans is not a 2900 player as massaged data might suggest.  

I feel the same way. My rating has been steadily increasing since I started playing. But I lost 70 points the day after I reached 900+ the first time. I've climbed back up now but it hasn't been easy.

I feel exactly the same.  I seem to have levelled off at around 900 (rapid).  Sometimes I drop below it and then get back above it but can never seem to pull away from it.  I really hope to get to 1000 one day but am beginning to doubt it.  For what it's worth I am 44 and only started playing just over a year and a half ago.  Maybe if I had started playing when I was younger I would have found it easier to break through the 1000 barrier.  However, I still love playing the game and try not to get too fixated over my rating - easier said than done though.

Opening principles: -Control the center squares. -Develop your minor pieces toward the center(piece activity is the key). -Castle. -Connect your rooks -Tactics,tactics,tactics: THE OBJECTIVE OF DEVELOPMENT IS ABOUT IMPROVING THE VALUE OF YOUR PIECES BY INCREASING THE IMPORTANCE OF THEIR ROLES. Well-developed pieces have more fire-power than undeveloped and they do more in helping you gain control. Now we will look at 5 practical things you can do to help you achieve your development objective.They are: •Give priority to your least active pieces.Which piece needs to be developed(which piece is the least active).Where should it go(where could its role be maximized) •Exchange your least active pieces for your opponent's active pieces. •Restrict the development of your opponent's pieces. •Neutralize your opponent's best piece. •Secure strong squares for your pieces. DON'T HELP YOUR OPPONENT DEVELOP. There are two common mistakes whereby you will simply be helping your opponent to develop: •Making a weak threat that could easily be blocked •Making an exchange that helps your opponent to develop a piece PRE MOVE CHECKLIST: •Make sure all your pieces are safe. •Look for forcing moves: Checks, captures,threats. You want to look at ALL forcing moves (even the bad ones) as this will force you look at, and see the entire board. •If there are no forcing moves,you then want to remove any of your opponent's pieces from your side of the board. •If your opponent doesn't have any of his pieces on your side of the board,then you want to improve the position of your least active piece. •After each move by your opponent,ask yourself."What is my opponent trying to do?"