In many cases, thinking that we are limited is itself a limiting factor. I've noticed this is true in ever facet of my life. When I was 14, I memorized pi to 50 digits with almost no effort. Later, I memorized it to 100, then 200. I realized at that point that I could memorize anything that I wanted to. I memorize phone numbers, credit card numbers, everything with almost no effort and not using any mnemonic device.…
I have similar experiences with (re)teaching basic math tricks and approximation to adults. "Oh, I wish I could to that but I suck at math" is a quite common response. I love the flash in their eyes when, after a short explanation, they make their first multiplication by 9 or division by 5 without the use of a calculator.
What I still don't understand is why some people are satisfied after learning the first trick while other (only 1/10th max) ask for more tricks. Shouldn't the idea of having learnt something new _always_ sparkle the interest in learning more?