A guy walks in to a computer store looking for a new PC. A custom built one catches his eye. A staff member notices this and walks over. He says, "Hi. My name is Spotty".
"That's an unusual name", says the shopper. "Anyhow, I was wondering if you offer some kind of service plan on these things.
"Oh yes", says Spotty. "We offer a great support plan on our custom built computers. All you do when you have a problem is bring the computer into the store and I handle all the maintenance and repairs myself, free of charge."
"Hmmm", says the shopper. "How good are you at that?"
"I always do my absolute best and I've never had a complaint", says the rather confident and smug Spotty.
So the shopper says, "In that case, forget it. I'm not interested."
To which the staff member replies, "Why not?"
"Because your support plan is Spotty at best.