Proverbs 14:10 - Joseph Benson’s Commentary on the Old and New Testaments

The heart knoweth its own bitterness The inward griefs and joys of men's hearts, though sometimes they may be partly manifested by outward signs, yet are not certainly and fully known to any but the persons themselves who are the subjects of them; or, as Bishop Patrick paraphrases the verse, “Nobody can know what another suffers so well as the sufferer himself; and he alone is privy to the greatness of that joy which springs from the happy conclusion of his sufferings.” The scope of the proverb may be, to keep men from murmuring under their own troubles, or envying other men's happiness.