The ability to do a task need not result in optimal performance. What else do you think is necessary?no
I believe it was Peter Drucker who said, "Anything worth doing is worth doing badly." That seems to speak to your inquiry in some way. None of us performs at our optimum all the time, and none of us are likely to do so. So, for me, there are two aspects of your inquiry that you might want to explore.
First is the question of whether optimal performance is necessary or desirable all the time. Do we really need to brush our teeth at optimal performance levels or do the dishes that way? Probably not! It might be interesting to think about when we do and don't care about this and when we should and shouldn't care about this.
Second is the question of what we need aside from ability to achieve optimal performance. I think motivation is clearly important. Without motivation, even satisfactory performance can be difficult for people. Another aspect of optimal performance is what people call "muscle memory." And I think of this whether the task is physical or mental. Athletes who train frequently and rigorously are creating a situation in which their muscles are retaining the memory of movements that will result in optimal performance when called upon. Since our brains are simply a collection of connected neurons, when we train them frequently and rigorously, the connections can move faster from neuron to neuron. This means that mental tasks can be performed optimally when needed.
So, there are a few things to think about. Do we want or need optimal performance for everything? How can we be motivated to perform optimally? How can we train ourselves to be at peak performance when we are motivated and this optimum is necessary?