Many people take the advise given by health books as seriously as they do advice from their doctor. Let's say that a health book advises you to drink 5 glasses of water a day. There is a misprint, though, and the book tells you to drink 50. Some people might actually drown from this advice!

It is a famous joke. It has a double meaning. Becoming too healthy could lead to obsessive or compulsive or fanatic and thus dangerous. etc.

This is a warning :) People should never take a crucial (impulsive) decision just after reading an article or a health book as they may damage their health or even die because of a misprint!!