Imagine meeting a pretty girl, all angelic-like cause she's dressed in white.
imagine falling in love with her and then finding out that your only competition is a buddy of yours.
imagine luke's horror when he found out leia was his sister.

obviously the force wasn't strong enough in him.
and if yoda knows all, why didn't he inform Luke of his incestuous ways?
WHY!?!?

imagine being Chewie...
....what a wookie.