This depends on a few factors, including what type of procedure you had done, what donor hairs were used, and how long it has been since your procedure. Although with experienced doctors this is rare, it can still occur sometimes if your physiology is at play. It is doubtful that an experienced surgeon would wrongly place the grafts by packing them too tightly. It is possible that some of the follicles were compromised during extraction, did not survive, and thus, will not grow. If it has been more than 6 months since your surgery and you still see no growth, I recommend returning to your surgeon to figure out what has gone wrong. You may require a hair transplant repair.