Not strictly a demotivational - i.e. not at all - but I liked it and couldn't think where else to stick it where it would do any good:
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'