I love this quote: Energy is the messenger, momentum is the message.
It also helps explain why the 45 ACP is still so popular a cartridge. Yes, it's slow. But it's also heavy, which means that the power expressed on the target is much more than the 9mm. Don't get me wrong, I enjoy both calibers, but for different reasons.
When it all boils down, energy=massXvelocity. Physics never lies.