What is the hardest question in the world?

Alright, I need some good hardest questions ever.
We've all heard the one, "Is the glass half empty, or half full" or "tell me about yourself" or "what is the meaning of life?"
I need some new ones, care to ask a really hard question?
(my answers-if anyone cares-to the above questions,
1. depends on whats in the glass---if its beer, half empty. The bartender always tops ya off.
2. stupid interview question...it's a trick question.
3. to live life to fullest)

so give me some good hard questions..