Brewer's: Shoe Pinches
No one knows where the shoe pinches like the wearer. This was said by a Roman sage who was blamed for divorcing his wife, with whom he seemed to live happily.
For, God it wot, he sat ful still and song, When that his scho ful bitterly him wrong.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894