A qualitative leap in chess

There is no formula or method that guarantees a complete understanding of what is happening in chess. However, there are those qualitative leaps in our chess performance. I remember in my transition from childhood to adolescence, I became more aware of the importance of weak square, offside piece and unccordinated pieces. So, everything was clearer for me. At the same time, my results improved. Later I learned other important topics, but that qualitative leap was perhaps the most important to me. How did you achieve your best qualitative leap in chess?

Currently there is a leap - however, in the wrong direction...

Okay so mine is a wired story.
So one day I was just posting in forums and posting when I stumbled upon this particular topic when someone was confused about the game lobby and kept ranting on how it was 'unfair' and made him lose 'a lot of points'. He was mainly confused about the color in the game lobby. So I wanted to help but I didn't know as well so i played 1 bullet game (I was very scared to play those days because I would lose rating. I just played mainly atomic and antichess and had 1300 ratings in standard chess. )
So I found the answer to op's question and surprisingly won the bullet game. IT gave me a weird feeling. I wanted to feel it again so I started playing chess again. My bullet rating went to 2000 eventually and my blitz and rapid ones too,

For me it was the discovery of online tactics.

when I was 17; I had a jump from 1900 fide to 2150; just by changing some parts in playstyle; and relearning endgames

I was just playing much blitz and bullet online (no classical at all) until a point where I had a national rating (same rating system as FIDE in Russia) of 1800 in Blitz and Rapid but 1300 (!) in classical. At this point, I had to play several important classical events, and eventually my national rating in classical got to 1750.
Now I really want the CM title so I'm totally updating my repertoire.

My chess strength increased when I learned to improve activity/mobility/coordination of my pieces.

My leaps occur once every four years.

The one that sticks out most for me is the concept of weak squares and complexes. I read two chapters about it in different books and still didn't quite grasp it, but then one day it was like someone flipped a switch and I started seeing those things light up. It was interesting that the weakness of a backward pawn became obvious at the same time, so there was something about weakness that I realized all at the same time. Those realizations are why I like studying chess I think. I've tried to imagine how beautiful it would be to have the same sort of realization about distant opposition. But it's amazing to me that we can stare at a wooden board with different color patterns and it's our internal knowledge that brings it to life like a virtual reality experience. It must be like looking at a book when you're illiterate and then learning to read.