if the shoe fits, wear it

A predominantly US variant of if the cap fits, wear it.

Why should Mr. Vanderbeek apply a general comparison to himself? Let those whom the shoe fits wear it.
[1773 New-York Gazette & Weekly Mercury 17 May]

If the shoe fits you, you can wear it a little wile [sic], Jack; but we won't quarrel about that.
[1876 W. G. Nash Century of Gossip 125]

Some one, devilishly inspired, had made a noose in the end and the knot was what is so widely known as a Hangman's knot. ‥‘There's an old saying, you know; if the shoe fits, wear it. The words might be made to apply to knots, I suppose!’
[1934 J. Gregory Emerald Murder Trap 260]

‘Zee, you're a know-it-all-crybaby-tattletale brat!’ ‘I'm telling Mommy that you said that!’‥ ‘What did Mommy say?’ ‘She said, “If the shoe fits, wear it!”’
[2001 Washington Post 13 Dec. C11 (Baby Blues comic strip)]

Related to: conduct; reputation

Bibliography of major proverb collections and works cited from modern editions is available here.

Also, if the cap fits, wear it. If something applies to you, accept it, as in These problems are hard to solve, and most people would need help, so if the shoe fits, wear it! This expression originated as if the cap fits, which alluded to a fool's cap and dates from the early 1700s. Although this version has not died out entirely, shoe today is more common and probably gained currency through the Cinderella fairy tale, in which the prince sought her out by means of the slipper she lost at the ball.