How do you know if you are doing a good job?

After the way my morning started off, I often wonder if I am doing a good enough job! I sent Bradley off to school in a bad mood because I made him read since he had a meltdown last night doing it and was sent to bed. So this morning I made him read instead of watching TV. Well you would have thought I told him I was going to cut his arm off and make him eat it for breakfast and then it went downhill from there. There was screaming and crying yet again over reading a book and I can't handle that anymore, I want to crawl back into bed and wake up and start the day over.

So how do you know you are doing a good job? If you send your child off to school sad and your sad, does that mean you have failed on this particular day?