Solving a problem that you know has a solution may require knowledge, but it is knowledge that already exists. Unfortunately – or, if you prefer, fortunately – many of the problems that are worth solving, that need to be solved, don’t come with that level of certainty.
In his book, How Life Imitates Chess (which, by the way, I highly recommend), Garry Kasparov has this to say about uncertainty:
Knowing a solution is at hand is a huge advantage; it’s like not having a “none of the above” option. Anyone with reasonable competence and adequate resources can solve a puzzle when it is presented as something to be solved. We can skip the subtle evaluations and move directly to plugging in possible solutions until we hit upon a promising one. Uncertainty is far more challenging. Instead of immediately looking for solutions to the crisis, we have to maintain a constant state of asking, “Is there a crisis* forming?”