This question was originally posted on Quora.com and was answered by Amy Chai, MD, Internal Medicine, MS Epidemiology The very best Lasik surgeon would NEVER trust ANYONE else to operate on his/her eyes. If you are the best surgeon, and you think nobody else is as good as you are, you would find that you are unable to operate on your own eyes. Therefore you must wear glasses. The same goes for a dentist. If there are two dentists in town, and one has beautiful teeth but the other has ugly teeth, which dentist is the better dentist? OF COURSE the dentist with the ugly teeth is the best dentist, because he is the one who gave the other dentist the perfect teeth. But the dentist with the good teeth could not do a good job, and the good dentist cannot fix his own teeth. Oncologists smoke because they know that everyone dies. Source