Originally Posted by Stu

Boredom is a core construct in existentialist thought, it's the essential human condition. When one is 'bored', they are confronting the nothingness of being. Life can be fun, and often is, but only because people are actively pursuing activities and interests, expending their energies, in the attempt to steer clear of the anxiety and dread that accompanies the realisation that everything's meaningless.

Of course, if you do not subscribe to existentialism, I'm sure you'll have another explanation for it.