I play a character until he gets defeated, then rest him.
Sometimes I need to put the character into a completely different situation, just to make it interesting again. For instance, I have a lvl 50 Fire/Savage tank that I can easily get burned out(yuk,yuk) doing fire farms, So I will exemp him through Ouro to say, lvl 19, and go burn up Lost and Trolls in Skyway. Just so I can remember what I loved about the combination. I do that instead of starting another Alt. (I only have 20 total over 4 shards).
11 of my 20 Alts are at some degree of incarnate. Playing only high level stuff gets boring. Incarnate power I am afraid trivializes too much. Then a defeat seems like "out of the blue, the game just cheated me, unfair". Time to do something different. This game is too good to get mad at because I got defeated once.