It was written down by Arthur C Clarke who was an author. It's just a rule of thumb really. I haven't looked into data on it but it seems like a common enough t

It was written down by Arthur C Clarke who was an author. It's just a rule of thumb really. I haven't looked into data on it but it seems like a common enough thing that there's something to it. As to why? I have no idea. Something lik: Older scientists are more conservative, therefore if they say something is impossible, they might just be out of touch with new developments. But if they say something is possible take it seriously because they don't use that word lightly.