Will I ever learn?

My latest painting is reminding me of a very bad habit of mine, being too timid! While I know, in watercolor, one begins light and goes darker, there is a happy medium. It takes me way too many layers to get as dark as I need to be. Why can't I remember that each time I sit down to paint? Still have a lot to do on the painting, it isn't a lost cause but I sure get mad at myself when I realize, once again, I am being way too stingy with the paint!