Suppose Hansen decides to plant the oak tree. Which result would be a cost?
The oak tree will use up more space than the irises would have used up. Hansen will get to look at the oak tree. He thinks it will look more beautiful than the irises would have looked.
Hansen is deciding whether to plant irises or an oak tree in his backyard. He wants to make his backyard more beautiful. But he also wants to leave space for doing fun things.
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 Hansen wants or needs:
The oak tree will use up more space than the irises would have used up.