Two Primary Problems
1. Most males have seen all the cool movies and have learned the technique already. Also, most American males think the ability to shoot - especially a handgun - is part of their genetic makeup. This can be even worse with men with some form of prior training (that didn't seem to help much, either.)
2. Hearing protection. Many guys are 'too tough' to wear hearing protection and therefore have a horrible flinch.
The best results I've had with 1. is demonstrating I can hit what I intend to hit. It usually works, but sometimes slower than other times.
2. is cured by asking them if they want to have hearing next year. Or simply getting them to 'try it' and they realize shooting is much easier when one is not anticipating being stabbed in both ears with pencils.
Neither work perfectly and women are much easier to teach.