You Don't Know Jack!
As I took my catamaran out of the Moorings charter fleet, I departed St. Maarten on Mystique, a 40' Leopard catamaran, in late November 2014 heading 400 miles northwestward towards the Bahamas, as a boat owner, I still had much to learn. Though I thought I knew a great deal about sailing, I knew little about my boat's idiosyncrasies, quirks and behavior during a long voyage. But mostly I knew my understanding of Mystique's mechanical and electronic systems was limited and rudimentary at best.
So, the question "Which is better? A generalist or a specialist? A person who is multi-talented / multi-faceted or a complete expert in one narrow, specific field? Someone who understands a little about a lot or a great Renaissance man - a polymath who possesses a depth of knowledge in all fields or someone with a general knowledge? Is it enough to possess a superficial knowledge in several areas? Or do I need to be completely competent sailor in all areas? Is an individual better served by striving to be a specialist, a generalist? Is it really possible to be both?
Breadth is often used in combination with or in opposition to length. For example, "the breadth and depth of his knowledge." Breadth is often used to describe the scope of someone's knowledge in a specific field.
Depth is often a measurement, but it isn't measurable when one refers to one's character, integrity and honesty. Then it is only revealed, displayed or exhibited in actions, interactions, feelings and words.
So what to know, how much to know and why know what you know? What's the point?
If someone ever stopped you and announced, "You don't know Jack Schitt!", you might have found yourself at a loss for an intelligent retort. Wanting to assure the individual that you, in fact, do know Jack, you , of course, need a thoughtful reply. A genealogical explanation (in yellow below) might demonstrate you do, in fact, know some Schitt as well as the depth and breadth of Jack's lineage.
In English a jack is by-name for a common person. In British English, jack is a very old (13th century) term to designate the average peasant - the man at the bottom of the social pyramid. See for instance colloquial expressions such as "every man jack".
In that sense it comes from Old French "jacques" which has the same meaning - "Jacques" being a very common first name in medieval France at the time. The revolt of the French peasantry during the Hundred Years' War was famously called the "
Jacquerie "because the jacques were all in arms and busy burning castles. It also gave English the word "jacket" that was then adopted back in French as "jaquette" (the lost "c" and the meaning of a typically classy suit is a tell-tale sign it does not come directly from Old French). During the British naval supremacy period, jack was also used to designate the average seaman. The word must have somehow passed into American English. See for instance "lumberjack" for "lumberman".
So in addition to the word "shit" symbol of something of little value, the use of jack here reinforces that meaning by referring to an average fellow of supposedly low level of sophistication or knowledge.
A jack-line is a kind of thin rope or line used for various purposes.
Jack lines or safety lines. Another very close way to see things is that "jack-sth" is used to denote a smaller version of this something. The OED says: applied to things of smaller than the normal size; [...] jack-bowl, jack-brick, jack-fish". So you get the idea: a jack shit is of even less value than a regular-size one
In British use the jack has been since the 17th c. (except under the Commonwealth) a small sized ‘Union Flag’ of the period (Union Jack), which has also been, since 1707, inserted in the upper canton of the ensign; hence, the name ‘union jack’ is often improperly applied to the union flag itself, when this is not carried or used as a jack. Every maritime nation has a jack of its own; this is usually, either as in Great Britain, †the German Empire, Sweden, and the United States, the same as the canton of the ensign, or, as in France and the Netherlands, identical with the ensign, only smaller". (Prof. J. K. Laughton.)
"A ship's flag of smaller size than the ensign, used at sea as a signal, or as a mark of distinction; spec. the small flag which is flown from the jack-staff at the bow of a vessel (formerly at the sprit-sail topmast head), and by which the nationality of a ship is indicated, as in British jack, Dutch jack, French jack.
Did American society ever fully appreciate the depth and breadth of this Jack's passion and purpose for life?