As title says, what mistake or attitude made you destroy your stats.
I'll start. It was long time ago, I had about 5k battles(most of them with KV-1, KV-1S, M6, tier 5-6 heavies mainly), playing on a bad PC, I had about 30 FPS with no graphics and even those would drop to nothing while in a bush/forest. So playing in bushes was a no-no for me.
I started to grind the French Light tanks (mainly because tier 5 ELC was broken as f) and when I reached tier 6 (in that period tier 8 was maximum tier for light tanks) the gameplay just wasn't fun for me, I was failing to do anything in the game so I said: F it! But instead of dropping the line I decided to complete what I started so each game I was rushing enemy base to kill some arties and wait for the next game. I wasn't affording premium account also so I had to do this for about 400 battles at tier 7 to reach tier 8.