@Fa5t3r - I think most people will be aware that their hands are being tested on a hard, physical activity though. It seems more common to me that people don't realize how much stress their hands come under during the typical modern day.
I think probably many hand spasms are caused by people typing without pausing or resting their hands, particularly on keyboards that aren't ergonomically designed.
Hands aren't meant to sit flat like they do when people are typing. They are designed to work best when they are facing each other (like they are when people are knitting, for example). Constantly keeping them in a bad position like that ends with the tendons that control the fingers becoming inflamed which can lead to spasms and pain.
I have to do a lot of typing, so I'm always very careful to try and keep my hands in good shape.