"Stop thinking!"

My voice teacher tells me this often, and it may seem absurd considering a few minutes before she is giving me all sorts of instructions and mental images about what to do to produce a really good sound. It never seems absurd to me, however. She sees my furrowed brow, the tension in my body, and it is clear that I am trying to over-control what will emanate from me much more easily than I imagine. That is just me all over. Sometimes I notice myself thinking about things, brooding really, and my hands begin to clench into fists. Shouldn't I just stop thinking? Just smile, relax, have fun. Is it not that easy?