A character completely misses a really obvious point for comic effect. The point is the sort of thing that any reasonable or informed person will spot and understand given a few seconds or enough information. However, the center of this trope is a person who, despite having all the time in the world and all the information, comes to a conclusion so wrong it's hard to be even further from correct. Commonly elicits a response along the lines of "that's not what's wrong here". Visual gags are often involved.