well for me i had two main issues,the first was my shoulders were a bit square causing a chicken wing and second was an aiming issue,my cue was placed slightly across the line of aim when down on most shots or i was aiming a hair to the left or right of where i was supposed to.(probably because my head was moving offline when getting down on the shot).the chicken wing would steer the cue slightly sideways on practice strokes/delivery and when i corrected the chicken wing,i still had the aim/cue alignment issue causing the cue to steer sideways once again.it was like a vicious circle.but when i started addressing both variables at the same time,my stroke started straightening out.so far it has been working but i will post here if i encounter more problems.
but someone else could have even more problems like sighting/dominant eye issues or stroke issues like jumping up on the shot,tightening the grip etc and maybe someone could be steering the cue for such a long time that the hitch in the stroke has been ingrained even when removing all the variables and needs practice of physical training to fix.or if someone is a complete beginner then of course he will not have a straight stroke if he just fixes aim and alignment.