There are four engineers travelling in a car -- a mechanical engineer, a chemical engineer, an electrical engineer, and a computer scientist. The car breaks down.
"Sounds to me as if the pistons have seized. We'll have to strip
down the engine before we can get the car working again", says the mechanical engineer.
"Well", says the chemical engineer, "it sounded to me as if the fuel might be contaminated. I think we should clear out the fuel system."
"I thought it might be an grounding problem", says the electrical engineer, "or maybe a faulty plug lead."
They all turn to the computer scientist, who up to then had reading his first edition SICP, and asked "Well, what do you think?"
"..."
"Ahem, Dr. Sussman?"
"Why am I reading this book?"
"Uh, I don't know?"
"So that the room will be empty."
"Wait a second, we aren't in a r... !"
And at that time the three engineers were Enlightened.