A builder gives you a low estimate to win your business on a big extension to your house. At the end he hands you the bill.
You have a sleepless night, a stiff drink and you decide to chalk it upto experience.
Quite possibly the worst analogy since:
“The little boat gently drifted across the pond exactly the way a bowling ball wouldn’t. “….and ….”John and Mary had never met. They were like two hummingbirds who had also never met”. They were taken from a High School exam paper.