A Thought to Think During Intense Workouts

I have been using my workouts to practice acting despite pain, fear, dread, etc. I have hunting for Thought(s) that help push me past previous limits. Interestingly I recently noticed that the Thought: “I can do this!” leads me to Feel discouraged and usually I quit. I assume this is because I don’t really believe this Thought.

I have better Results from the Thought: “Nothing has gone wrong here,” but it isn’t energizing. Do you have additional suggestions on Thoughts that might help push me in moments of physical discomfort (or even pain)?