Suppose Erik decides to plant the tulips. Which result would be a cost?
He will save some space. The tulips will use up less space than the birch tree would have used up. Erik will give up the chance to look at the birch tree. He thinks it would have looked more beautiful than the tulips.
Erik is deciding whether to plant tulips 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 Erik wants or needs:
Erik will give up the chance to look at the birch tree. He thinks it would have looked more beautiful than the tulips.