It's like a drug. Like when you're around a person you're attracted to and they'll say or do something that triggers shot of chemicals to your brain and all you can think about is how to get more of that feeling, which sucks if it wasn't intentional on their part and they're not interested in you because now you have to fight against basically a drugged state to shut that shit down while trying to be normal around them. Jerking off produces the same feeling but there's something missing that makes it less satisfying than being with another person.