There is no more difficult art to acquire than the art of observation, and for some men it is quite as difficult to record an observation in brief and plain language.

Osler stresses two linked disciplines at the heart of good medicine and good thinking: first, the trained ability to notice accurately (observation), and second, the equally demanding ability to translate what one has noticed into clear, economical language. The remark implies that perception is not passive but cultivated through practice, and that sloppy or ornate prose can betray sloppy seeing. In clinical settings, this is a warning against both diagnostic error and poor case-records: if observations are not captured plainly and briefly, they cannot be tested, shared, or acted upon. More broadly, the quote champions precision—of attention and of expression—as a professional virtue.