It&#x27;s because you understand that programs, when you write them, are frozen at time zero, that it&#x27;s s-expr tentacles are ready to accept inputs, and when they get an input, they contract in computation and, for long lived programs, emit <i>new tentacles</i> that no programmer ever wrote.<p>(If you can write reliable tentacles and dress them up so that people want to touch them frequently, you can become very, very rich.)