When you look at the sky and see a big black cloud, you could reasonably conclude that rain is imminent.
But once you take into consideration past, present, and future weather conditions on all continents, combine this info with a detailed analysis of global weather patterns in the know universe, your prediction will probably become less certain.
Facebook, Google et. al. want to know everything about everybody. It's in their nature. Paradoxically, this wealth of information will sooner or later prevent them from making reliable predictions. The more they know in general, the less they know for certain. It's much like approaching lightspeed: The faster you go, the more impossible it becomes to actually reach the speed of light.
You want to mess up the mighty AI's algorithms? Set YouTube on autoplay and go on a holiday. Write a script that googles for random words. Once a week, go to a public library and log into your Facebook account. Cookie galore!
At the very least, this should lead to some very interesting online ads.