Two guys are in mental instituition.
One guy says, “Hey, I know how we can break out of here!”
The second guy says, “Oh yeah, how?”
The first guy says, “I've been thinking about really hard ever since I saw that big search light that goes around every night from the airport. Here is what we do. First, we steal a flashlight.”
The second guy says, “Hey, we don't have to do that, I've got one here that my kids sent me!”
The first guy says, “Great, then meet me out in the courtyard, near the wall tonight, after everyone goes to bed.”
So they meet out by the wall after dark. The guy with the light asks the first guy. “Just how will this plan work?”
The first guy says, “It's like this, you shine the light up on to the top of the wall. I'll climb up the beam of light to the top. You throw up the light and I'll shine the beam down for you to climb up. Okay?”
The second guy ponders the plan a second and then says, “Hey, just a minute. I know what you would do. I'd get you up on top of the wall and throw you up the light. Then, as I was half way up you'd turn off the light! Do you think I'm crazy or something?”