I like to fill 3 bobbins before starting a project. When they run out ( always mid seam, mind you), I wind 2 or 3 more. I sew on a Featherweight and IF I AM PAYING ATTENTION! I can generally hear the difference when I run out. Not always - but it is a help sometimes. In the early years - I did the same thing you do on a very regular basis. Sew and learn, I guess. It is a maddening situation!