Among the things I routinely do wrong is thread my Singer treadle sewing machine. Threaded incorrectly, stitching produces a clotted mass of threads on the back.
My machine is a Singer model 66-1 with red-eye (also known as red-head) decals, produced some time after April 18, 1921.
I can tell the earliest possible date from the serial number, using ISMACS Singer serial number database.
Properly threaded, it runs like a dream. Do it wrong, however, and EEEEEEEEEEEE!!!
I usually orient the bobbin correctly, but just in case I note here for future reference that the thread should exit the bobbin counter-clockwise when I drop it in, i.e., at the same angle as the slot in the bobbin case. Useful (and amusing) blog post about bobbin orientation may be found here.