Wondering

I was talking with a friend recently who was upset with herself for being annoyed about something that really shouldn't annoy her. Sadly I know all too well what she means. I've found myself angry or annoyed or even hurt by things that I really should have just let go of immediately. I do wonder why we are like that. Is it a girl thing? Guys don't seem to get annoyed nearly as often. Are they better at getting over things or are they simply better at pretending to?