If you combine quantum many-worlds ideas with the line of thinking that they were originally designed to eliminate, namely 'observation collapsing the wave function' you get the somehow both obvious and absurd idea that there is only one observer in the world in which you find yourself and that is necessarily you. It is a way of reconciling the faith in universal contingency with the odd necessity adhering to the cogito. Well, you might say, clearly I am the sole observer of my universe, but my universe is wholly imaginary, is merely an imprecise subjective projection of the real universe. And where is this real universe located, the one in which the event of imagining is really happening? Just where you think it is, only it is nothing like you think it is because it is full of other observers each of whom is seeing a different world, and in each of these other worlds there is a something resembling you cognising which exists as an objective fact or ongoing event, a happening, while only here in the world you actually inhabit does there appear to be no such (objective) fact. All of this grows progressively more incoherent the more you think about it. The problem seems to lie in taking your own experiencing as some kind of fact in a world. That is the way that we think about everything which is, and what could have any more title to existence than what says 'I am', or the prime imaginer in an infinite regress of positings.