Pretty sure it has something to do with some people's saliva being better than others.
Otherwise, the main thing I'm pretty sure is true is... once you go to dentist for a cleaning, brush twice a day and floss every day for a month. After that, it's best to keep doing so, but your teeth's enamel should be as good as they'll be again.
Beyond that, don't brush your teeth immediately after eating or eat after brushing (wait 30 mins - 1 hour for each). Try not to snack too much, as that can keep your enamel more vulnerable throughout the day.
Other than those, I believe fillings do wear out and need to be redone eventually. Damage is more or less permanent to your teeth enamel once it's damaged too far.
My brother regularly had cavities, but ever since he switched from sugary drinks to regular water throughout the day, the cavities stopped. I personally had no cavities filled, but did have 2 cavities forming because of the same sugary drinks. I reversed those with good brushing and flossing habits.
I now brush 1 time most days, sometimes 2 if something feels wrong. I also floss every other day because I'm lazy, but the bad breath gets really bad if I go any longer than that between flossing.
This is with one of those sonic toothbrushes (it's a knockoff of name brand, but it works) and alternating between string floss and a water flosser. I also once used a plaque/tartar scraper about 4 years ago, but didn't seem to actually do anything. Its been nearly 8 years since I went to a dentist, and nothing feels or seems off.
...Typing this out, I realize you probably are aware of all this. But well, on the off chance you weren't, maybe it'll help going forward. I squandered a lot of teeth care + orthodontics because I was never made aware of what I'm supposed to be doing. Until it was too late. It at least hasn't gotten any worse since I looked into teeth care.