There's also a lot of variation between teeth. Smooth teeth are less likely to develop caries than teeth with deep crevices, and some people have brittle teeth that break easily.
It's not just how well you brush your teeth.
Another factor is what you eat/drink. If you drink sweetened drinks all day, your teeth are probably going to suffer, and I doubt that brushing teeth twice a day is going to make up for it.
I also have multiple teeth being resorbed, a weird thing that the dentist says nobody knows why it happens, and it has nothing to do with dental care.
Take a look at some older people. They may not have lost all their teeth, but you can see the crowns and false teeth.