Fillings for example always degrade and need repairs after X years. Drilling and filling even the smallest cavity puts that teeth on a lifetime progression to bigger and bigger fillings, eventually a root canal, eventually an implant.
Cavities, on the other hand can be arrested (stopped), and if small can even be remineralised. Yes, most dentists don't tell you that!
Careful monitoring and patient education on the other hand can lead to permanently keeping that natural teeth, as our teeth are living and can heal.
My personal lived experience: a dentist told me I must fill 2 cavities six years ago. I got a second opinion. That dentist told me I should wait, focus on oral care, chew xylitol gum, and use a toothpaste with novamin.
Both cavities have "arrested" and need no restorative work.
Disclaimer: Not a dentist. Listen to your dentist you trust, and get second opinions if you have doubt.