You meet someone, things seem peachy, a couple of weeks pass and YOU ABSOLUTELY KNOW it's not going to work BUT you stay in it anyway.
Discuss.
Been there. We both knew there was no way we could build a good relationship based on on just sex alone,
... so, after 3 years and many latenight booty calls later, ...we ended it.
J/K. Can't say I've been there.
If I know it's not going to work, ...I won't stick around. That would seem selfish to me. Better to move on and let them move on as well, ...both parting as friends before it turns to hostility, resentment, and hatred on one or both parts.