吃力不讨好 [- - bù tǎo hǎo]a thankless task; arduous but fruitless; be a fool for one's pains; do a hard but thankless job; look for a needle in a bundle of hay; work hard but get little result:
•¶ 要是你想帮助他这个人， 那将是吃力不讨好。 If you try to help him, you will be a fool for your pains.