Having experience repairing fabrics, but not nearly an expert in it, there is something to be said for the art of it. You need to know how much of the surrounding fabric to anchor your stitches to, how often to double back to lock in the stitches, and very importantly to make sure you're making the stitches tight enough. I'm sure that there's some far better advice out there, but if you sick with it eventually you'll learn to make solid stitching by hand.