The phrase "when the shoe fits" or "if the shoe fits, wear it" is an idiom used to say that something said or suggested about a person is true, and that the person should accept it as true. It means if a description or criticism applies to someone, they should acknowledge it rather than denying it. For example, if someone is called a cheater and the phrase is used, it means if the accusation fits, then accept it as true. This idiom is commonly used to imply that a remark or judgment is accurate for the person being addressed, even if it might be uncomfortable or unwelcome.