keep one's nose to the grindstone
Fig. to work hard and constantly. Son: I'll never get good grades. I might as well not even study. Mother: Don't give up yet. I'm sure that if you just keep your nose to the grindstone, you'll get the results you want. Mary kept her nose to the grindstone while her friends were out enjoying themselves.
nose to the grindstone, have/keep one's
To work hard all the time. The image, transferred from tools that must continuously be sharpened, is a vivid one and has been used since the sixteenth century. “This Text holdeth their noses to hard to the grindstone, that it clean disfigureth their faces,” wrote John Faith (A Mirrour to Knowe Thyselfe, 1539).