There are two reasons most experts would agree on. 1. The cut itself must compliment your personality and face shape. For example: Remember Jennifer Aniston's cut? That was a great haircut because it complimented her specific facial characteristics. The cut would not have looked as good on Angelina Jolie. 2. A great haircut looks good even as it grows out. In other words, it should look great between services. Hair grows at a rate of 1/8" per week. Cutting the hair every 4-6 weeks maintains its shape and placement.