If you forgot if you drank the glass of water, no harm. Same with salt. If you forgot if you took your Paracetamol pill, accidentally taking another one would

If you forgot if you drank the glass of water, no harm. Same with salt. If you forgot if you took your Paracetamol pill, accidentally taking another one would leave you with permanent liver damage. It's like looking into the sun: normally, you flinch/blink away and are safe. But if you stare, and suppress or your reflex isn't working, you'll catch a life-long blind spot burned into your retina. The therapeutic margin is just insanely small for anything OTC.