Fermat said he had a proof.
However impenetrable it seems, if you don't try it, then you can never do it.
The greatest problem for mathematicians now is probably the Riemann Hypothesis.
I really believed that I was on the right track, but that did not mean that I would necessarily reach my goal
Just because we can't find a solution it doesn't mean that there isn't one.
Always try the problem that matters most to you.