Every multiple exposure image is an experiment. You aim the camera and press the button, anywhere from two to 2,000 times (I tend to stick with ten or fewer), but there is no way of knowing how the camera will combine the images. Sure, there are various modes: like Average or Bright, but you can never know exactly what you’ll get, even if you’re using an Overlay option that gives you a transparency of shots already recorded.
This is as it should be. Art is not about control, and there is a difference between being intentional and trying to nail down a particular outcome: in yourself, the work, or the viewer. Madeleine L’Engle thought of it as the difference between creating art and crafting propaganda. That pretty much works for me.