I agree with John S here. More so than with other cameras, a rangefinder demands monogomy. It requires you to have an intimate knowledge of what your camera and lens can and can't do. This only comes with familiarity and practise.
I myself use quite a few cameras (of late, mostly DSLRs), and find it fairly straightforward when going between them. Sure, there are differences in handling and usage, but broadly speaking the experience is much the same.
But, when I pick up the Leica M8 - especially after not having used it for a while - I really have to stop and think about what I'm doing. You get so used to zoom lenses and AF, it can be difficult to go back to a fixed prime lens and manual focus. It requires a very different approach.
John S mirrors Henri Cartier-Bresson, who famously talked about the Leica as an extension of his mind and eye. However, to achieve that sort of rapport, you need to be very familiar with the camera. You need to feel totally comfortable with the way it feels in your hands.
Most of all, you need to 'know' your lens so you can position yourself to get the shot. Some old Cine footage of H C-B taking pictures showed him tip-toeing back and forth like a dancer. He was moving all the time. This goes against the 'modern' approach, where you stand still and just zoom the lens to get the desired framing.
J M Hughes