I never had nits in all my days in school, hitchiking around the world and living in communes.
But in the last few years my kids get them constantly and I get a few now and again too. As soon as you think you've got rid of them the kids pick them up again from their friends and school.
The shampoo does work to some extent but I wouldn't recommend using it. It has bad chemicals in it and some strains of nit have built up a resistance to them.
For us it's Tea Tree oil, hair conditioner and wet combing with a metal nit comb every three days. For our son it's quick and easy and most of the time he doesn't have any but with our daughter, who has beautiful long blond hair, combing out her hair is a major event. When we had foster kids we had four kids to comb every three days.
Basically it's a losing battle but if you don't keep up with it then they become infested and that's not pleasant.
Only when the last tree has died and the last river has been poisoned and the last fish has been caught, will we realise that we cannot eat money