Value: Where does it come from?

Pastor Steve has recently talked about the things or people we try to get our value from other than God and it really affected me. It brought to light how often I depend on others to give me my value other than God which is obviously a let down most of the time. So, since I started to grasp this concept of course I have to be tested in it! Last weekend I made a castle cake for a lady that I thought turned out pretty well, but she wasn't there when I set it up and later that day I got an e-mail describing all the things to felt was wrong with the cake. She said it would take her days to list everything that was bad and she wished she hadn't paid me. She said the bottom two tiers were the same size (which they weren't), that the pink was the wrong shade, that the cake was the wrong flavor (which it wasn't) and the list goes on. Obviously this wasn't the perfect ending to my week and it brought a lot of feelings of failure and doubts on continuing doing the cake thing. So, as I am sitting in the parking lot of Wal-Mart reading this e-mail from her and this feeling of defeat washed over me and I laid my head on my steering wheel and cried. Through the tears God spoke to me and amazingly enough the tears lasted no longer than a minute. God picked me up, dusted me off and sent me into the store to continue buying stuff for the next cake adventure. Even as I am checking out I am thinking, "What am I doing putting myself through this stress and making myself vulnerable to people's disapproval AGAIN?!" all the while praying for God to give me my value through people's critiquing. It's not as thought what the lady said didn't affect me, because it did and the thoughts still creep up on me from time to time, but the peace the surpasses all understanding is my covering and the cake-ing continues!
P.S. There were issues with the cake order for Wednesday too BUT I am still getting ready for this weekends cakes, I don't even understand this perseverance....