In reference to the fantastic idea sponsored by the "war on drugs" that one should just say no. A sizeable part of the population thought (and still think) that this statement was naive, badly thought out, and just plain Rude. The american population obviously did not like being patronised quite so much by their leaders, and so coined the phrase "just say know". In other words know the difference between propaganda and fact. Be sensible. Above all exercise your freedom and make an informed decision for yourself.

Although the term came about as a result of a campaign against drugs, it can be applied to just about anything (or should say everything?). There is no such thing as enough knowledge.