Generally, I feel there are two ways to lose money.
The first one is by making mistakes (and there are many ways), but you have to be able to determine when a mistake has been made in a certain situation and recognize when the situation comes up again, thereby cutting down your losses or increasing your winnings. When I first started playing, I was playing too many hands and was getting nowhere - the more hands you play, the higher the possibility of making mistakes.
The second one is by suckouts. Unfortunately there is nothing you can do about this, unless you have made a mistake by betting incorrectly. This generates whining about so-called bad beats, which should simply be ignored. Forget them and get on with the next game.