If corn rows (hair very tightly braided usually in Afro Style) are too tight, they can over time literally pull out hairs by the roots. This usually happens at the front hairline and/or at the back hairline (at the back of the neck) where an anchor knot (big knot) is tied; this is called Traction Alopecia.  Do not tie knots too tight!  Traction Alopecia can also be caused by incorrect hair weaves that pull out the hairs they are anchored to. (During day-to-day activities and sleep a weave can put strain on the hairs it is woven to). 

At eMPower Hair  we see many customers with this problem and are usually able to help with therapy to try and re-grow the hair, thicken rounding hair, or replace hair with a system if required.