Your body actually is rather capable of making you acutely aware of most health conditions that require intervention.
By the time you become aware of a cavity, it might be pretty well advanced, and you may be looking at a crown or even root canal vs a filling.
A cavity requires intervention before your body tells you it does - by the time it does, you’ll be in excruciating pain and basically lose half a tooth to the drill. If you fix it before then, it’s much easier.