Why all the Health Testing? Don't you know your lines?

In the decades I have been breeding canines, if i had a penny for every time i heard another breeder say " I know my lines," I would be a millionaire. Can you know your lines? I am not a wizard who can look at a dog and see recessive genes. The fact is that breeders who say this don't have this superpower either. They are guessing. Instead of guessing what a