An overcooked steak, an undercooked salmon filet, overly salted food, a food allergy, a hair . . . OK, a chef is understanding of these mishaps and will quickly seek to amend them. However, if you're not a fan of onions, but onions appear on the plate and you didn't request "no onions," better just eat around them unless you are deathly allergic. Chefs feel quite enraged by perfectly good food being sent back.