I picked up a small booklet from 1979 in a yard sale. It's called STITCHOLOGY..has a lot of interesting thing in it.
Under the chapter for Breaking Thread is
Needle in backwards
Upper tension too tight
Debris in tensions
Incorrect needle
Lint pack in lower race
Thread too thick
Needle too thin
Poor thread, or thread too old
Burrs on thread handling mechanism
Spool holder in backwards
Material too thick
Check all of these, and if you are still confused. I'll
write you all what it says on each page for all of these.