"A classic example of emergence lies in the flocking behavior of birds. A computer simulation can use as few as three simple rules (along the lines of "don't run into each other") and suddenly you get very complex behavior as the flock wends and wafts its way gracefully through the sky, reforming around obstacles, and so on. None of this advanced behavior (such as reforming the same shape around an obstacle) is specified by the rules; it emerges from the dynamics of the system."
Andrew Hunt (The Pragmatic Programmer)
Something to remember when designing systems and thinking about usability.