There is a knock at your door, it's me.
I say; "Hi! I just mowed your lawn! I'm just looking to collect my fee for the use of my services."
You look at your lawn, note the clippings around the edges, and determine it was indeed mowed. You can't recall how much it needed mowing, but the job was obviously done. "Well, I didn't ask you to do it, but it obviously needed to be done. How much do I owe you?"
I smile and reply cheerfully, "One Thousand dollars." Your jaw drops.
"How could mowing my lawn possibly be worth $1000?"
"Well, I did a lot more than mow the lawn."
"Well, I did some charity work, mowed some of your neighbor's lawns, painted a house, walked some dogs, babysat, and did a number of other things that I can't specify, but I assure you, they benefited you indirectly."
"And you expect me to pay you for those things?"
"Well, you DID get your lawn mowed."
"But I didn't even ask you to do that! I'm not going to pay you!"
"That wouldn't be a good idea. If you don't pay me, I'll send some of my friends with guns over and they'll take you away from your family and life, and lock you in a room for a few years; then they'll make you pay me anyway."
"You can't do that! I'll call the police!"
"No you won't. My friends ARE the police."
Who am I?