Survival is not the impetus for all rational thought. And if you would only take some time to notice, an idealist world view almost always subverts the imperatives of survival under the imperatives of spiritual ideas.
Just look at buddhism. Is there anything more anti-thetical to the survival instinct as this? More so with its more radical incarnation of zen - the philosophical basis of bushido, the samurai warrior code.
It really is quite simple. Any individual with a rudimentary reasoning faculty can instantly discern immutable principles - like cause and effect or the duality that exist within everything in nature. And it doesn't take additional thought to conclude that what he sees operating in nature must also be operating within himself.
Finally, there is this unusual bias in people towards the scientific. And at the heart of the natural sciences is the empirical method. The thing is, what is empirical is NOT NECESSARILY sensory. Sure, extenal stimulit, by which we are able to 'know', passes through our senses. But still, rational thought occurs in the mind, where all external stimuli is sythesized into human experience.
So, if the amount of people who feel aliens are watching in their showers is statistically significant, any reasonable individual couldn't simply dismiss the notion, could he?
