burn one's fingers

To suffer an unpleasant or ruinous consequence (especially the loss of money) for some action, often such that one becomes unwilling or reluctant to do it again. During the boom times, countless would-be investors put everything they owned into shady investment deals, and most of them ended up burning their fingers badly.

Harm oneself, as in I'm staying away from risky stocks; I've burned my fingers often enough. Some believe this expression came from a legend about a monkey who gets a cat to pull its chestnuts out of the fire (see cat's paw); others hold it is from an English proverb: "Burn not thy fingers to snuff another's candle" (James Howell, English Proverbs, 1659). [c. 1700]

To hurt or harm oneself. Some writers believe this term comes from the old story about a monkey who persuades a cat to pull its chestnuts out of the fire (see cat’s paw). Others believe it comes from an old English proverb stated by James Howell in 1659 as, “Burn not thy fingers to snuff another man’s candle,” and by Samuel Palmer in 1810, “The busiebody burns his own fingers.” The connotation of interfering in someone else’s affairs has vanished, and the modern cliché means simply to get hurt by performing any hazardous or foolhardy action.