Possibly what you're missing is the intermediate steps? We know about most of them. Do you have any problem, for example, with the transition from a lobe-finned fish to a tetrapod?
When I first looked at electronic circuits, I thought who the heck can possibly understand this complicated network of transistors and resistors and capacitors. Once I learned a little more, of course, I realized it can all be divided into sub-circuits that perform particular functions, and it's just a question of recognizing the elements. People can understand the most extraordinarily complex things, but only in pieces.