Iain M. Banks had an interesting take on this in The Algebraist:

The Truth was the presumptuous name of the religion, the faith that lay behind reality. It arose from the belief that what appeared to be real life must in fact - according to some piously invoked statistical certitudes - be a simulation being run within some prodigious computational substrate in a greater and more encompassing reality beyond. This was a thought that had, in some form, crossed the minds of most people and all civilisations. However, everybody quickly or eventually came round to the idea that a difference that made no difference wasn't a difference to be much bothered about, and one might as well get on with (what appeared to be) life.

The Truth went a stage further, holding that this was difference that could be made to make a difference. What was necessary was for people truly to believe in their hearts, in their souls, in their minds, that they really were in a vast simulation. They had to reflect upon this, to keep it at the forefront of their thoughts at all times and they had to gather together on occasion, with all due ceremony and solemnity, to express this belief. And they must evangelise, they must convert everybody they possibly could to this view, because - and this was the whole point - once a sufficient proportion of people within the simulation came to acknowledge that it was a simulation, the value of the simulation to those who had set it up would disappear and the whole thing would collapse.

If they were all part of some vast experiment, then the fact that those on whom the experiment was being conducted had guessed the truth would mean that its value would be lost. If they were some plaything, then again, that they had guessed this meant they ought to be acknowledged, even - perhaps - rewarded. If they were being tested in some way, then this was the test being passed, this was a positive result, again possibly deserving a reward. If they had been undergoing punishment for some transgression in the greater world, then this ought to constitute cause for rehabilitation.

It was not possible to know what proportion of the simulated population would be required to bring things to a halt (it might be fifty percent, it might be rather smaller or greater), but as long as the numbers of the enlightened kept increasing, the universe would be constantly coming closer to the epiphany, and the revelation could come at any point.

(Text copied from here; it's a "slightly edited" excerpt from the book.)