The first small section below is from the Transformation chapter of Humility and Formality, by Ælflæd of Duckford, concerning being responsibly present:
If your lifelong drinking buddy becomes king treat him like the king. Support him in the appearance of being the king. Remind him that he is the king. Drop the drinking buddy behavior and expectation.
Sobriety would be the ability to be serious, thoughtful and responsible when its needed (and often on short notice, which is probably the main reason serious inebriation is such a danger to a responsible person's reputation and development). The opposite of sobriety as I was thinking of it would be the careless, goofy, giddy, heady mindset that's pretty easy to come by, and fun and useful, but which people need to know how to turn off when it's time for a sober-minded person to make a decision or to help someone else.
Gunwaldt and I used to go play video games when we were young and had $20 and no kids. We'd go to Putt-Putt when tokens were on sale, and we'd play for hours and go home. Arcade games aren't like Nintendo-on-the-couch. When you're standing up and leaning into a box bigger than you are, with nothing in your peripheral vision but black-painted plywood, the adrenaline rush is very different from anything on TV at home. There's also the loss-of-token factor, where winning (although still worth little) is REAL (even if it's 12.5 cents real). Driving a car right after three or four hours of that can be different. It's not a game anymore, but after hours of leg-numbing adrenaline and "death" and valiant near-misses, things don't seem so real.
We had to practice snapping out of it.
When people are SCA royalty, there's some energy build-up from attention, responsibility, deference, POWER (even if it's $125 power), and some handle it very well, while others get giddy, heady, and careless.
Same with officers and autocrats.
Sobriety is the observance and avoidance of that "OH BOY the rules don't apply to me" thinking that can cost people social points.
Because of the United States' puritanical roots and the nation's experience with federal prohibition of alcohol, Americans hear "sobriety" and think of all kinds of 20th century stuff ranging from cranky great grandmas through "revenuers," bootleggers and AA meetings.
The word "sober," though has a much greater depth than "not drunk," and that's where we should be looking for this virtue. No one needs to be sober in the meaning of dead-serious and humorless all the time, but unless one has the ability to know when to be serious and to put humor aside, he won't be much use in an emergency situation, or when a problem calls for calm, far-reaching analysis.
"Temperance" is a related virtue, also tainted for me and some others by 20th century associations with devil rum and such. But to be temperate, instead of too hot (too quick to anger, too quickly distracted, too inpetuous), is clearly useful and virtuous. Although temperance is often used to discuss not eating or drinking too much, that's not all it means.
There are times to party and times to be prepared to be available, as an autocrat, an officer, or a peer.
—Ælflæd of Duckford