I've been disappointed a few times when I tried to solve a promising-looking puzzle, given up, and waited eagerly to hear the answer, but no answer came because the asker revealed they don't know it and nobody could solve it. This made me feel like I wasted my time looking for something that wasn't there.
By default, I expect questions posed to be puzzles with nice solutions that were crafted for me to find and enjoy. It's fine to pose a puzzle whose answer you don't know or an intriguing question you tried to solve yourself without success. But as a solver, I'd like to be warned that the solution might be impossible or ugly or require brute force.
This largely seems to be a miscommunication due to the similar formats of puzzles and actual questions.
So, I'd like to propose the following policy:
When posting a question in puzzle form to which you don't know the answer, you must say so. Otherwise, it is assumed by default that you are posing a puzzle to which you know the answer.