bite off more than one can chew, to

To take on more than one can accomplish; also, to be too greedy or too ambitious. Versions of this cliché, warning against taking on too much, date from the Middle Ages and appear in ancient Chinese writings as well. A lighthearted more recent example is Ogden Nash’s (from “Prayer at the End of a Rope,” 1939): “Let me not bite more off the cob than I have teeth to chew; please let me finish just one job before the next is due.”