If (a) the game gets really, really boring, or if (b) I get too, too tired, or if (c) I just do not feel like playing any further, or if (d) something more important comes up... I will (a) find something more interesting to do; or (b) go for a rest; or (c) follow my feelings and leave the game; or (d) attend to those matters of more import that are at hand. No matter what decision I make in (a), (b), (c) or (d) - it means I will lose the game as a matter of fact and as the result of intent because I am purposely no longer there to play it.
I try always to keep in mind, whether for play chips or real money, that poker is a game I want to enjoy when I play. If I can not do that, if I can not enjoy it - for whatever reason above, or for whatever other reason - then why play on?
Some people can not walk away from a game of poker. To them, poker is like a case of beer to which the player is addicted. The addict can no more walk away from poker than the alcoholic can leave the beer. When that happens, the game controls the player, not the other way around.