I Love Surfing the Internet, Reading, Learning

Yeah, but how on Earth does the internet know about you. It's starting to get really creepy. It's like it's reading my mind or something. I know ads and stuff are based on your search history mostly, but things I only think about and not search for an ad pops up for it. For example, I feel like I may need to start wearing glasses again. All of a sudden there is an ad telling me where to get glasses. This is something I have not yet searched for.