MindHacks vs the BBC who sadly had not done their due diligence on the question of why we're unable to tickle ourselves no matter how hard we try. The answer? Turns out to be another evidence that the world you inhabit is not the same world I inhabit, it is a 'Matrix' simulation, but one of our own making, grounded periodically in sensory input:
a scientific paper [pdf] entitled 'Why can't you tickle yourself?' addresses exactly this question.
The science of this is quite well known (in fact, it was featured in the original Mind Hacks book as Hack #65) but in summary it seems that the brain simulates of the outcomes of actions based on your intentions to move because the actual sensory information from the body takes so long to arrive that we'd be dangerously slow if we relied only on this.
This slower information is used for periodic updates to keep everything grounded in reality, but it looks like most of our action is run off the simulation.
So it is true: Life is but a Dream!