these have always (and probably still are) been mine:
1-not being consumed/focused on one Forex cross, stock, option, Futures contract etc....looking at too many trading vehicles
2-overtrading
3-trading on impulse or emotion and no true strategy
4-revenge trading "I'll win/get it $$$ back"...has always put me in deeper holes...
NOTE: one of the best things I have done is...not scalp trade, not execute manual orders...set them and 'go mow the grass'...