I've been healthy all my life, apart from a short bout of asthma when I was a kid and the usual cough and cold, flu and fever that never last longer than a few days. My immediate family have all been healthy as well. No crippling infections or cancers, no diabetes or hypertension, no congenital defects or blood disorders, none of the stuff described as 'poor prognosis- death in five years or less' on our textbooks.
If there's one thing systems after systems of pathology has shown me, it's how much I've been taking my own good health for granted all these years. I'd learnt and read about heaps of diseases I never thought could exist- mainly because as a healthy person, you tend not to think about what could happen if a single little component of your body, like a gene or enzyme, was abnormal or diseased. It's just life as normal.
Maybe it's a normal human thing to take things for granted.