吃老本 live off one's past gains [past glory]; live on one's fat; rest on past achievements; rest on one's laurels
吃力 (费力) strenuous; laborious; entail strenuous effort; be a strain 他学习吃力。 he has difficulty in his studies. 那位伤员吃力地站了起来。 the wounded soldier has made efforts to stand up
吃力不讨好 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