Because memory and sensations are so uncertain, so biased, we always rely on a certain reality - call it an alternate reality - to prove the reality of events. To what extent facts we recognize as such really are as they seem, and to what extent these are facts merely because we label them as such, is an impossible distinction to draw. Therefore, in order to pin down reality as reality, we need another reality to relativize the first. Yet that other reality requires a third reality to serve as its grounding. An endless chain is created within our consciousness, and it is the very maintenance of this chain that produces the sensation that we are actually here, that we ourselves exist.
Haruki Murakami, in 'South of the Border, West of the Sun'