A conspiracy theory is an invitation to an exciting alternative reality where nothing is quite as it seems. There is fun to be had defying conventional wisdom, sifting through signs, uncovering lost knowledge and secret plots. But we don't generally believe stuff just for the fun of it. For us to really believe something it has to seem plausible. How can we be so sure that our journey off the intellectual beaten path and down twisting trails of conspiracy theory has led us to the truth, while the scientific mainstream is deluded or deceptive? Sometimes all it takes is our own overly optimistic brain telling us we understand the world in far greater depth than we actually do.