There are two modes of performance: A practice mode, in which you assess what your doing, and a live mode, in which you let go of self-conciousness. In the first few minutes of this clinic, Kenny Werner shares some powerful thoughts about improvising without inhibition. His comments about practicing versus playing (after about nine minutes in) are especially noteworthy.
If you are an improvisor, or aspire to be, set aside time to view this master class.