Speech is a performance. There are many similarities between music performance and public speaking. Many elements of the musician’s mindset, attitude, and preparation for a performance apply to any presentation, any audience, and any circumstance.
In the music world, we use the 120/80 principle when preparing for a performance. That means if I prepare 120 percent of what I want to accomplish on the stage, the outcome will be about 80 percent of what was expected. During the live presentation, a number of things could happen:
Just ask any presenter or performer after the presentation whether they achieved 100 percent of their performance goal. Nearly all would say no; there is always room for improvement.
In terms of piano practice and performance, there is no such thing as “over-rehearsing.” There are thousands of ways to interpret and express each single phrase in music. Just imagine the millions of combinations and possibilities that can be demonstrated in a 10-minute presentation. It is impossible to over-rehearse millions of options.