When i draw i line it constatly stop in between making it impossible to draw a continous line. Why?

I've attached an Illustrator course to the thread -- maybe that'll be helpful, or maybe another user will have a thought. I'm not an Illustrator user myself, but I'd think a more detailed description might help someone pinpoint the problem -- i.e. what tool are you using, exactly what are you drawing (straight line, curved line, multi-segment line, etc); stop in-between what, beginning and end of the same line, or between segments in a more complex line, etc; could you be lifting your finger off the mouse/pad without realizing it?..