Why Does Overshoot Occur in Electronics?

[likephysics]

Why does overshoot happen. For example in electronics, a square wave oscillating between 0-5V, overshoots 5V by a small margin.
When the power supply can only supply a max of 5V, how can the signal overshoot. I guess the same goes for ground (signal going below zero).

 

[rcgldr]

Inductance in the circuitry causes this, electrons have some momentum and it requires special circuitry to counter this. I don't think it's possible to make perfectly square waves, but near square waves with rounded corners and no overshoot are possible.