A lot of times, people want to get a snack, though sometimes it is in a jar of some kind. When they try to grab for whatever is in the jar, they will get their hand stuck because of the way that they have a grip on the thing in the jar. This is a Comedy trope in which when you grab the contents of a jar, your hand winds up getting stuck, because of the way you have a grip on it. This trope can come with An Aesop about greediness if the character is unable to get their hand out of the jar because they're holding too much food.