One friend's answer to being an asshole

I have meetings with writing groups monday and tuesday this week. We leave thursday for ten days. A friend wanted to meet to discuss a wedding shower we will throw for another set of friends who threw both of us showers. She wanted to meet wednesday. I said sure. Robin was like, "what are you thinking?!" I thought as an exercise to not be an asshole I should just stop overbooking. So I told her we should reschedule for when I get back or talk on the phone. I explained about my work colleague and my fear of being an asshole all the time. This friend's response was that everyone, not just parents, are assholes sometimes. That did not make me feel better. Is it just part of being human to be an asshole?