Awhile back, I picked up "Harriet the Spy" from a thrift store. I knew my mother enjoyed the book as a kid, so I thought I'd check it out. I'm only part way through, but I already relate to Harriet. She watches people. Yes, sometimes she does it through the skylight of their apartment and that's creepy, but she also pays attention to details when she's out and about.
People are hilarious. They each have stories to tell and secrets to keep. If you're watching closely, they will tell you some of their stories and give some of their secrets away. It's human nature to want to be noticed. We all want someone to listen.