The answer ties back to the life cycle of a hair. There are three stages of hair growth. In order for the electrolysis treatment to be effective the hair must be in the first stage called anagen. At any given time there are only 20 - 30% of hairs in the anagen stage. Since it is difficult to know which stage any given hair is in just by looking at it. Many hairs will be treated that are not in the anagen stage and will regrow. This is why electrolysis requires repeat treatments and a bit of patience. However, if you stick with it, you will be rewarded with results.