I'm going to decide to keep my mattress and box spring instead of trading it as I agreed
Why are you not going to honor the agreement you had?
I have made my decision, I would rather keep it.
You should not break agreements with people, it's rude and a sign of disrespect. You need to do what you agreed to.
Who cares about all that. I want to do as I please, fuck them.
You would be angry if someone did not honor an agreement with you. It is important that you honor this, others will not trust you if you don't.