If one understands why a certain phenomenon exists
if one understands exactly how something works
if one understands the foundational truth of a situation
that understanding allows one to act effectively in any manifestation of that situation.
If one fundamentally understands why a human being makes a purchase decision, this understanding will inform every business decision he makes — from branding, marketing, website design, product collections, ad creative, font choice, product design, email campaigns, etc.
In the same way that if one understands that if he will be hurt if he falls from a great height, it allows him to act wisely on cliffs, buildings, platforms, windows, etc.
Therefore it is the fundamental understanding that matters.
Often, you will find I write on this blog from this perspective. Asking, what is the fundament of the situation at hand? What is it, which if I understood, would allow me create success in a given domain?
It is understanding that matters. The specifics of how to do something, while obviously important, is secondary.
Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime.