A saddle stitch is two needles and one thread, worked through the same hole from both sides. It is slower than any machine, and it holds when a machine stitch would unravel — which is why the best leatherwork is still sewn this way.
The apprenticeship that teaches it is just as unhurried. Years are spent cutting, skiving and edging before a needle is trusted to an apprentice, because a stitch is only as good as the leather prepared for it.