Here is a bookend prompt for you to consider. A bookend prompt is (as far as I know) something I created. It is comprised of two prompts. You should use both, though you can use them in either order. Use one as the beginning of your writing and the other as the last line of your writing.
Left Bookend Prompt: He had all the answers.
Right Bookend Prompt: Wait...what just happened?
So, what do you envision between those? A know-it-all scientist who discovers that the laws of physics aren't always accurate? Or maybe a boyfriend who thinks he know what his girlfriend expects of him...only to be surprised by something she does.
Remember, you can also reverse the prompts, so that the story starts with confusion and ends with your character feeling assured of his own knowledge. Good luck, and keep writing!