your eyes are bigger than your stomach

(one's) eyes are bigger than (one's) stomach

1. One has taken more food than one is actually capable of eating My eyes are always bigger than my stomach when I go to all-you-can-eat buffets! Can't finish your meal, huh? I guess your eyes were bigger than your stomach!
2. One has taken on more than one can reasonably handle. Your eyes are bigger than your stomach if you think you can get all this work done by the end of the week.
See also: big, eye, stomach
Farlex Dictionary of Idioms.

your ˌeyes are bigger than your ˈstomach

(informal, humorous) used to say that somebody has been greedy by taking more food than they can eat: Can’t you finish your food? Your eyes are bigger than your stomach!
See also: big, eye, stomach
Farlex Partner Idioms Dictionary
See also:
  • (one's) eyes are bigger than (one's) belly
  • belies
  • cooking for one
  • drive (one) out of office
  • force (one) out of office
  • force out of office
  • give (one) (one's) head
  • give head
  • give somebody their head
  • give someone their head