For instance, my "home" positions on the keyboard vary, but the keys my fingers land on at rest follow the natural curve of my hand. My hands are spaced out a bit more on the keyboard than the home row (with my right pinky reaching to the Enter key), and I instinctively use different fingers to strike keys as required by the other keys to be typed. For instance, with "different", I would use my left middle finger to hit "e", but then with "keys", my left hand rotates a little bit to the right so that I can reach the "y" with my index finger, and end up hitting the "e" with my ring finger. This happens seamlessly; if I type "different keys", by the time I'm about to hit the last "e", my hand is already rotating to bring the "y" in range.
I suspect if I studied it for awhile, I'd be able to see basic principles in it, but at least on the surface, there is no apparent logic. It just works. And it works pretty well, enough so that typing with the home row method seems extremely cumbersome.