Whenever you prepare for a story you don't want any plot point to come across as an Ass Pull. But depending on the needs of the story you don't want to spend more time than necessary to establish a vital skill a character may possess that will prove useful, such as an establishing scene that will be used as a Chekhov's Skill. Compare Suddenly Always Knew That when a character suddenly reveals that they had the skills as they are using it, instead of any sort of Foreshadowing. Compare Pastimes Prove Personality, Let's Get Dangerous. Examples of Chekhov's Hobby include: