Stitching is where every earlier decision either holds up or falls apart. A cut piece of cloth becomes a wearable trouser here, and this stage has the most opportunities for small errors to compound — a slightly uneven seam allowance, a rushed waistband — into problems you'd actually notice when wearing the finished garment.
Construction starts with the internal structure: darts, pocket bags, and the waistband facing go in before the outer seams are closed, since these are hardest to fix once the trouser is mostly assembled. Front and back panels are then joined at the inseam and side seams, followed by the waistband, fly, and closures. Each stage is checked before moving to the next rather than assembling everything and inspecting only at the end.
Seam strength matters more in a trouser than in most other garments, simply because of how much stress the fabric is under with every step — sitting, walking, bending at the knee. We use seam allowances and stitch types chosen for durability at the stress points specifically: the inseam, the crotch seam, and the waistband attachment all get reinforced stitching rather than the single pass used on lower-stress seams like hems.
Pressing happens throughout construction, not just at the end. A seam pressed open immediately after stitching sits flatter and cleaner than one pressed only after the whole garment is finished. This is slower, but it's the difference between a trouser that hangs cleanly and one that looks slightly off no matter how it's worn.
The finished trouser is inspected once more before it's approved — checked against the pattern measurements, checked for stitching consistency, checked for any flaw that made it through construction. Only after that does it get a Lot Number, tying it back to the exact yarn, dye batch, and cloth run it came from. That's the whole process, start to finish: yarn to dye to loom to cloth to cut to this. A SLOOM trouser, woven first, cut second.