Lay a mamian skirt out flat and the arrangement looks lopsided. All the pleats are gathered into the two sides, while the front and back each keep a broad, entirely smooth panel. Why leave the two most visible areas unworked? Because those panels are doing a job the pleats cannot do.
The skirt has to open when the wearer walks, climbs a step or sits down. That opening is supplied by the pleats, which unfold sideways. But an opening in a garment is also an opening to look through, so something has to stay flat and stay put while the sides expand. The two smooth panels do exactly that: they overlap slightly at the centre front and centre back, forming a covered door that stays closed no matter how far the pleats spread.
What the pleats are actually storing
The cloth is not cut to fit the waist. A woven width is much wider than a waist, and rather than trimming the surplus away, the maker folds it into the waistband. This is the same economy as a garment made from rectangles: keep the full width of the loom, and use folding rather than cutting to reconcile it with a body. Nothing is wasted, and the hem keeps the straight edge the loom gave it.
The pleats are paired and face each other, one folding left and the next folding right towards a common centre. If every fold leaned the same way, walking would drag the whole skirt slowly around the body, and after a few steps the flat panel would no longer sit at the front. Facing pairs cancel that sideways pull. They open together and close together, so the smooth panels stay where they were placed.
The fold lines have to be set with starch, heat or a pressed crease, otherwise the pleats forget their arrangement after the first wash. This is the same problem a shirt collar solves with an interlining: a fold that must be reliably found again is given a physical memory. On a skirt that memory is the difference between a garment with two crisp panels and a soft, evenly crumpled one.
Why two flat panels, front and back
One panel would cover the front, but a turning body exposes the back. With a flat panel at each end, the two overlap zones alternate as the wearer moves: when a step opens one side, the opposite panel is still lying flat; when a gust lifts a hem, there is a second smooth surface behind it rather than a row of gaps. Getting this right is a matter of width — each panel must be broad enough to overlap the other with some margin left over.
Those panels are also where embroidery goes. A motif spread across pleats would be broken into strips and swallowed every time the skirt closed, while the flat field stays legible from any angle. It is no accident that the most decorated area is also the one least rubbed by movement; where a garment wears out first is almost always a fold, an edge or a point of friction, not a smooth centre panel. Dense stitching is safer where the cloth is least stressed.
There is a structural reason too. The flat panels join the two pleated groups like two crossbeams. When the pleats fan out, they pull on the waistband from both sides; without a stiff, unpuckered section front and back to take that pull, the waistband would ripple into waves. The smooth part is the member that holds the whole arrangement square.
What changes if the panels go
A skirt pleated all the way round behaves quite differently. Every fold opens and closes with each step, so there is no stable surface at all, and a lift of the hem exposes a shifting set of gaps. That is a perfectly good garment for other purposes, but it answers a different question. The mamian skirt is built around a covered opening; an all-round pleated skirt has no opening to keep covered.
The contrast with a side slit is instructive. Both garments need to give the legs room, and both refuse to simply make the skirt wider. One gets that room from a vertical opening guarded by an overlap; the other gets it from horizontal folds stored in the waistband. In each case the solution is a controlled gap, not extra cloth.
You can test the arrangement in two seconds: hold the skirt by the waistband and shake it gently left and right. The pleated sides open and close visibly, while the two smooth panels barely move. That stillness is the whole design. The pleats supply the movement so that the front and back do not have to.