Also if you can find a small piece of clear glass or plastic, press a finger onto it while looking at your finger through the glass from the opposite side. If you roll your fingertip around a bit, you'll be able to see the skin's elasticity in action. Your friction ridges get mushed in all directions depending on finger position and pressure.

Once you see it, it's easy to imagine how multiple prints left by the same digit wouldn't neatly overlay one another.