Some people, and you may be one of them, play looser and get overconfident just because they are head on their cash. You have to learn your play style and stick to it, regardless of how much money is in front of you.
I see nothing wrong with setting a goal and then taking a break. Many poker books will gripe at you for setting a "stop-win" condition, but if it's how you stay profitable and works for you, go for it.
Personally, I set a goal sometimes like reaching so many FT points. Other times I set a timer on myself. If I go over two hours, I'm hopping off for a few minutes, even if the game is good, so I don't lose focus.
I normally play 4-6 tables. |