It's rude to back out on plans with friends.
Timmy had planned to go on a camping trip with friends, but learns that his cousin is coming to visit him that same weekend.
Timmy wants to spend time with his cousin.
Timmy invites his cousin to come camping with him and his friends.
Timmy cancels his plans with his friends.
Timmy's friends enjoy their time with him and his cousin and have a great time on their camping trip.
Timmy's friends are very disappointed.