burn one's fingers
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]