It is easy to tell if someone has even a rudimentary understanding of the human mind.
A person who understands the mind keeps a notepad and pen, to write with, on their person. All images, ideas and insights seem like they are monumental and would never be forgotten...at the moment they occur. But they are gone a short time later, forgotten forever, or at least forgotten until they reappear briefly a few years or decades later.
This phenomenon was first pointed out to me by Bucky Fuller in an idle conversation we had one afternoon.