Yup. I tried to work out why once, and I think I came up with something like that you don't want to pick 1, 5 or 10 because those sound so non-random. So maybe you choose seven because it's far from both 5 and 10. And maybe you pick 7 instead of 3 because 7 is considered a lucky number.

Of course, if you really want people to think you're a mind reader, you should practice subtly making them think of a given number. Certain magicians are very good at 'reading peoples' minds' that way .