Which is the toughest question to answer?

Wow the question itself is the toughest question to answer. Every unanswered question is a tough question "?". It's OK if you cannot answer the question because it simply means that you don't know the answer or answers. But it is tougher and painful for who has the "unspoken" answer. "It's already at the tip of the tongue" as the saying goes but still there are forces that pull it back to freely utter the fact, the truth on thing being asked. It's is whether because of shame, pride, belief, concealing something else or whatever it may be. It's tough, tougher, and toughest for that person who knows the answer, has the chances to answer and choices to answer but never speak up. ;)