>> If you take advice on infectious diseases from an ophthalmologist, you're going to have a bad time.
> Why am I going to have a bad time for following his rules and advice?
You're not, you're just being over-literal. Most ophthalmologists are sensible people who will give guidance outside their fields that comports with the guidance from medical professionals in that field. That sounds like your ophthalmologist. However, if you find an ophthalmologist who blatantly contradicts the guidance from areas far outside his field, then that's when "you're going to have a bad time." The reason for that is you've likely found someone who doesn't respect the limits of his own knowledge and experience.
> Why am I going to have a bad time for following his rules and advice?
You're not, you're just being over-literal. Most ophthalmologists are sensible people who will give guidance outside their fields that comports with the guidance from medical professionals in that field. That sounds like your ophthalmologist. However, if you find an ophthalmologist who blatantly contradicts the guidance from areas far outside his field, then that's when "you're going to have a bad time." The reason for that is you've likely found someone who doesn't respect the limits of his own knowledge and experience.