Why Do I Throw Completely Winning positions
I play 10mins is that good?
Well, this is a good time control, but as a beginner you’d get much more value from playing slower games (e.g. 15+10) and analyzing them thoroughly !
As of your original question : when you think you’re winning you might become lazy and not think much about your moves. Never forget your opponent will keep fighting until the end. So question all their moves, find how they could turn the tables and identify a winning plan :)