The FUE procedure removes hair from the back of the head, so it can’t grow back. The amount of hair that can be removed is limited. If too much hair is removed, as in this person, the back of the head becomes thin and see-through as a result of the depleted donor area.
The number of FUEs that can be removed depends upon many factors. Most importantly, the original donor density must be measured by the surgeon before recommending FUE graft numbers. If too many grafts are removed from the donor area, balding in the back of the head (as shown here in this photo) occurs.
The initial problem, prior to a hair transplant, is that most patients want more hair moved, and surgeons are motivated by the money they receive for taking out more FUE grafts. So, without good planning, the donor area is often over-harvested, producing balding in the donor area (as shown in the photo below). I can state with almost 100% certainty that 5500 grafts would produce donor over-harvesting in 98% of the population because the original donor density in 98% of the population will not support this number of grafts (see here: https://newhair.com/donor-area/).