From time to time I will learn of something that piques my interest. Normally, I will just look this up on wikipedia. But occasionally, there will be no wikipedia article. Not even a red link on the disambiguation page. If this is a highly esoteric topic, fine, I can live with that. But it's unsettling when it happens for something that is relatively accessible.
This always leads to something of a minor existential crisis. Wikipedia is such a heavily ingrained extension to my mind that the fact that it doesn't know about everything shows cracks in the very fundamentals of my world view. It's a deeply disturbing notion that if wikipedia doesn't know about this particular topic, it could be oblivious about any number of topics.