If you are called up a stage unexpectedly, you do not have to be rehearsed and perfect. Olivia Colman gave a great example of that last night at the Academy Awards ceremony. Her acceptance speech is genuine, authentic, empathic. It leaves a mark.
The same is true for every time we expect to be called up. If we work towards perfection, if what we care about is ironing out all the kinks, if that becomes the focus of our job, chances are we are putting energy, care and effort on the wrong thing. And most of all, we lose in personality.
(For a great example of an official speech delivered in a far-from-perfect fashion, this keynote from 2015 by Elon Musk is as personal as it is inspiring).