What does the "tragedy of the commons" refer to?

Xcerpt from mrs. wilson’s cook book- broiled hamburger steak mary a. wilson broiled hamburger steak do not fry or pan hamburger steak made from flank of sirloin. place meat in bowl and add; three-quarters cup of moist bread crumbs, one onion, minced fine, two tablespoons of parsley, one teaspoon of salt, one-half teaspoon of paprika, one egg. mix, form into flat cakes, brush with salad oil; place on baking dish. broil in gas broiler for eight minutes, then place in hot oven for seven minutes longer. spread with desired butter and send to the table in a baking dish. this will give a delicious flavored meat in place of the usual dry, tasteless cake that is frequently served. what happens when the flat cakes come out of the broiler? a) they are ready to be served. b) they should be lightly salted. c) they are to be placed in a hot oven. d) they need to cool for fifteen minutes.