Because I was convinced that otherwise, Jesus would kidnap and kill me.
The unforgettable little story "Jesus Understood" from Uncle Arthur's Bedtime Stories, a collection of Christian morality tales, is the reason why.
The opening sentence of "Jesus Understood" establishes the tone: "Little Bobby was crossing a busy city street when a big car came and knocked him down." (Although it is not specifically mentioned, there is probably some subtext here containing a Valuable Lesson about looking both ways while crossing the street.) Poor Bobby seems doomed from the start, but then we're shocked to learn he's damned to boot! See, Bobby winds up in the hospital rooming with his old pal Tommy, and Tommy knows who Jesus is, but Bobby does not.
Because Bobby is probably going to die, Tommy tells Bobby all about Jesus and how He'll take you to Heaven if you just ask Him. Bobby remains unconvinced that "a big Gentleman like that" would ever "listen to a little boy like me." Tommy explains that there's an even easier method to capture Jesus's attention: "Just put up your hand--like we do at school--when He comes through the hospital. They say He comes through every evening when the lights are turned down." (This always led me to wonder: if Jesus is like a schoolteacher--raise your hand and he'll choose you--what happens if you answer the question wrong?)
That night, Tommy says it is "time," and, instead of alerting a medical professional, he urges Bobby to put his hand up. Bobby, however, is too weak to keep his hand raised. Tommy fixes the problem by propping up Bobby's hand with a pillow. The last lines of the story read: "In the morning the little hand was still there. Bobby was dead, but Jesus had understood."
Always keep your hands down, just in case.
Source: Maxwell, Arthur S. "Jesus Understood." Uncle Arthur's Bedtime Stories. Vol. 1. Washington, DC: Review and Herald, 1964. 18-20.
Buy Uncle Arthur's Bedtime Stories: Volume 1