Why do I still care about grades?

Just checked them and now I'm annoyed. I got a B on a take home. I should be okay with it. I graduated and will stay that way unless I fail something (hello, corporations). I should let it go and focus on that more important thing in front of me. I spent over half of the week that take home was due in Florida. But participation was something like 20% of our grade and I participated so I still feel shafted.