Will Power

I read somewhere that the more you use your will power the weaker it is. It's not like a muscle. If you use it, the more likely you are to break when it's tested again.

Today I went to DSW and did not buy any new shoes.
(If you think that this is because I didn't find any I wanted, you are either dumb or a boy)
Then I came home and made home made pizza for dinner and cut it into smaller portion sizes than I had originally intended to make the calorie count more reasonable.
(If you think that this wasn't difficult, then you are seriously underestimating how much I love to eat)

This worries me.
I have had two strong tests of my will power this afternoon alone.

Do you think knocking on wood covers stuff like this?