They are told. Everyone has a limb length discrepancy which is causing them a problem and needs treatment. How they can correct something out of place by manipulation (the forces to do do so with ligaments in place doesn’t make sense) and to expect so called manipulation to withstand physiological bending, rotation, movements doesn’t jibe.
I have patients who were under chiropractic care for their rotator cuff tear for months until money ran out. After repairing the torn cuff patient gets better and asks what was the chiropractor doing and my answer is I’m not sure.