Suppose Lamar decides to eat the vanilla custard. Which result would be a cost?
Lamar will give up the chance to eat the peanuts. The peanuts would have been healthier than the vanilla custard. Lamar will get to eat the vanilla custard. Lamar thinks vanilla custard will taste better than peanuts would have.
Lamar is deciding whether to eat peanuts or vanilla custard for an afternoon snack. He would like to eat something tasty, but he is also trying to be healthier.
Before you decide to do something, it is often helpful to list costs and benefits.
Costs are what you give up or spend when you decide to do something. Costs involve giving up things that you want or need.
Benefits are what you gain or save when you decide to do something. Benefits involve gaining something that you want or need.
This result is a cost. It involves giving up or spending something that Lamar wants or needs:
Lamar will give up the chance to eat the peanuts. The peanuts would have been healthier than the vanilla custard.