It takes me like ten or twenty minutes into each session before I actually start focussing. Usually in that time I've made a stupid call down, which is what causes me to then think, "Shit I should play better". If I could play well from the start, I'm sure each of my sessions would benefit.
That is so me.

Calling down aggro donks (esp when OOP) too light. Always thinking people who 3bet are doing it "light" and so making 4bet bluffs that just get shoved on.

Tilting when I'm running good. This results in me calling down too lightly, being WAY too aggressive and starting to get too confident with strong but not nut hands.