The Variance! (Skill /Luck) when i explain poker to people who know little about it this is what i often mention first because if a person is considering getting into the world of poker but they are a poor/bad looser then i tell them they should perhaps persue another hobby.
If there is the slightest chance that you could loose a hand even with good odds
and many outs then you have to except it could still happen/will happen and you should just take it on the chin if it does.
The obvious replies i get are like ..."You can still loose with the best hand whats the point of that!!?,i will stick to betting on Horses thanks!"