I've found anecdotally that the mind has a feeling of a physical block, whether real or imaginary, to when you do not want to do something. Technically, all that exists to overcome this is the decision to ignore this feeling and do the action. That's it. Meaning you can likely do a multitude of things clearly and efficiently if you wanted, but you choose to not, for whatever reason.
The likelihood of you having this kind of concentration or willpower is unlikely, so substitution via stimulant is what most people settle for.
