Why does it seem your car NEVER comes to a complete stop?

It's weird, but you can come to a complete stop with the brake ON, but after that if you let go, the car STILL wants to move forward! It's not even a downhill either. In fact, it was a flat straightaway leading INTO a small hill! And it's not just there, but any stop light, stop sign, etc. What causes the car to move on it's own after you completely brake it and sit for a few seconds? Just curious.