If The Shoe Fits Meaning

(idiomatic) If it has all of the characteristics of a thing, it probably is that thing.

Example:   "Everyone keeps calling me a bully!" "Well, if the shoe fits..."
1901, Horatio Alger, Young Captain Jack, ch. 18:
  "Do you mean to insult me by that?" he roared.
  "If the shoe fits you can wear it."
  "I'll knock you down for the insult."