Khaled Abu Toameh has been talking to various Palestinians, and has heard that all three Palestinian men who committed attacks in Jerusalem so far this year had a similar motivation: they had been in trouble for something, they had become a source of embarrassment, and they had to redeem their honor and that of their families. What better a way to do so than to murder Jews, and if they died in the process (as they all did) they'd have the further honor of being Shahids.
I've said this before and I'll continue to say it until it changes: Palestinian society is severely sick. Not every Palestinian, of course, and it doesn't have to be permanent, but right now, that's the situation.
(Hat tip: Kai).