It is the difference you cannot see — until you have worn a shirt for five years.
Single-needle stitching means one line of thread instead of two. It takes about twice as long to sew. It lasts about three times as long to wear. Most modern shirts skip it because it is inefficient. We build our shirts around it because it is honest.
Look inside a mass-produced shirt and you will usually find double-needle seams: two rows of parallel stitches, spaced a few millimeters apart. They are fast to sew and, for the first few washes, look sharp. But the two rows tension slightly differently over time. One line pulls; the other buckles. The seam warps. The shirt loses its geometry.
The slower way
Single-needle stitching lays a single line of thread down one side of the seam, then another single line down the other. Two passes, one needle. The stitches sit further apart, breathe with the fabric, and stay parallel through years of washing. The line stays true.