It is used a difficult technique to stitch the bag along asperity of the inlay sandwiched between main material and lining.

If that stitching gets deformed even a little or the ditch made by stitching is not parallel, the bag can’t be transformed properly.

And, if snap button position is misaligned even a little, the bag can’t be folded. It requires the skill to pound a snap button into a precise position.