avoir les yeux plus gros que le ventre

Etymology
Literally, “to have the eyes bigger than the stomach.”

Verb

 * 1) to have eyes bigger than one's stomach to take more food on one's plate than one can eat
 * 2)  to bite off more than one can chew to try to do too much; to take on or attempt more than one is capable of doing
 * 1)  to bite off more than one can chew to try to do too much; to take on or attempt more than one is capable of doing

Conjugation

 * see