sitting out when you're way ahead (bankroll management question)

^ agreed. position is the nuts.

The only time you should ever leave a game you are winning in is if you start to feel uncomfortable for whatever reason. Whether it's because you suddenly have half your roll on the table (at risk or not), a better player has position on you, or you are losing focus. I mean if you are perfectly comfortable with your game and don't have a problem sitting at 100NL $1000 dollars deep with a fish then do that. If you are $10 deep at 2NL against a reg and don't want to lose that then stand up.

Any time you are playing not to lose you are going to make mistakes.