I try not to say something is "too hard". I always mentally correct that to just "hard", because "too hard", to me, means "I quit". Some things really are "too hard", though. The whole class of computing problems called "NP-Hard" are kind of one-directional, and, with sufficient size, they are too hard to solve before the universe will collapse into heat death. There are physical tasks that can't be accomplished because sufficient force would destroy the components, which makes them too hard as well. In general, though, I try not to apply the label "too hard" to something just because it is a huge challenge or because it is beyond my current abilities. Those things are hard, but they are still possible. That's what I mean.
Mokalus of Borg
PS - Stop me if I ever say "too hard" when I mean "very hard".
PPS - Also, I consider this a case of language pedantry rather than positive thinking.