Suppose Pablo decides to plant the birch tree. Which result would be a cost?
Pablo will get to look at the birch tree. He thinks it will look more beautiful than the hydrangeas would have looked. The birch tree will use up more space than the hydrangeas would have used up.
Pablo is deciding whether to plant hydrangeas or a birch 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 Pablo wants or needs:
The birch tree will use up more space than the hydrangeas would have used up.