The increasing dichotomy of us:
Two flat surfaces lie together fairly well - there are not too many protruding areas or recessed areas to cause a poor fit or incongruence. Two surfaces with their own individual contours and shape may be able to be adjusted, manipulated, wiggled around to be made to fit fairly well. Usually this results in some chafing or eroding of one surface by the other to make the fit better. The larger the projections and concavities, the more finagling and twisting and re-shaping become necessary. But once the two are made to fit fairly well - the joined surfaces are more strongly joined. They are less apt to slip apart because the shaped areas interlock more so than two flatter surfaces.
But, what if you could increase the depth or height or overall dimensions and complexity of the contours of the two surfaces, while still maintaining congruence? What if there were a way to shift around the edges of the forms from the inside to find the best fit, the most harmonious coincidence of one boundary to the other. Then, increasing the differences in the shapes of the two more, rather than less, would lead to a stronger union between the two. One edge bulges out in fantastic ways, the other yeilds to follow the mirror contour. One draws back and receeds and the other follows to fill the void left. The boundary between two such surfaces could become so deeply and complexly intertwined, that each side lends strength to support the other's beautiful shape. These would be very difficult indeed to separate.