So I view mechanics like "once is all you get" as a game convention.
It is like saying in D&D that the thief cannot keep rolling 'pick locks' endlessly on the same lock. That check means "you fiddled with it until you reached an end state in any attempt to pick it, there's nothing more you can do."
Gygax's AD&D has a prohibition on retries for picking locks (I think you can try again when a level is gained), for finding and removing traps, for trying to open locked or magically held doors (assuming STR is high enough to permit a check in the first place) and for bending bars and lifting gates. Also, I think - though maybe it's not as clearly stated?, I haven't gone back to check - for searching for secret doors.
Forcing ordinary doors and listening at doors permit retries, but there are other costs built in (eg chance of wandering monsters due to noise made and/or the passage of time).
In Burning Wheel the ban on retries ("Let it Ride") is interesting because it cuts against the GM as well as the player.
it helps if it already on the map, and you have a sentence or two about it, even though you have to take a breather to create something or pull something off the shelf in order to supply details if the players choose to explore it.
This is based on my observation of doing this for decades with multiple groups of players. I first noticed this when I switched from using the World of Greyhawk to Judges Guild Wilderlands in the early 80s. The players considered what happened to be more fair knowing that many details were there ahead of time. That I wasn't just making naughty word up to spite them.
you do run the risk of things just becoming uninteresting. If the players are hankering for social intrigue and big-city action, and all the table coughs up are airless rocks and TL2 worlds with no spaceport and a law level of A, they are probably going to think that's boring. Anyway, I don't think it is a problem at the scale of a sector/sub-sector map because it is such a vast region, SOMETHING interesting can be scared up. But that again speaks to how much Traveler leans on "the ref can add stuff that makes things interesting" (though to be honest, TAS, patron tables, random encounters, bureaucrats, etc. goes a long way, space is rarely a snooze for long).
From Classic Traveller (1977), Book 2 p 36 and Book 3 pp 8, 19:
When a ship enters a star system, there is a chance that any one of a variety of ships will be encountered. The ship encounter table is used to determine the specific type of vessel which is met. This result may, and should, be superseded by the referee in specific situations, especially if a newly entered system is in military or civil turmoil, or involves other circumstances.
[T]he referee should always feel free to impose worlds which have been deliberately (rather than randomly) generated. Often such planets will be devised specifically to reward or torment players.
Adventurers, as they travel about on planets, also have random encounters with an unpredictable variety of individuals or groups. . . . Some random encounters are mandated by the referee. For example, a band may encounter a guard patrol at a building while in the course of visiting (or burglarizing) it. The referee is always free to impose encounters to further the cause of the adventure being played; in many cases, he actually has a responsibility to do so.
Putting to one side the terminological contradiction in the last quoted paragraph (ie mandated/imposed encounters are not
random ones), the idea is fairly clear: the Classic Traveller referee is at liberty, and indeed is encouraged, to implement setting and situation in such a way as to generate interest (whether in the form of reward or torment!) and to propel the action forward.
I don't think the word "fair" is used at all. Book 1 (p 3) says that the referee "may also indicate possible quests for the characters, using rumor, barroom conversation, or so-called general knowledge" and that s/he "must settle disputes concerning the rules . . . and act[] as a go-between when characters secretly or solitarily act against the world or their comrades". Book 3 (p 44) says that
Above all, the referee and players work together. Care must be taken that the referee does not simply lay fortunes in the path of the player, but the situation is not primarily an adversary relationship. The referee simply administers rules in situations where the players themselves have an incomplete understanding of the universe. The result should reflect a consistent reality.
Whatever the notion of "sandbox" encompasses I think that Classic Traveller play has to fall within its ambit. But that same RPG system envisages GM intervention into setting-authorship and situation-framing so as to make sure things are interesting and that play is furthered.
To my mind, the main difference I see between Classic Traveller as presented and as I approach it is that I don't generate so much of the star map in advance. I began with, and from time-to-time added to, a stock of pre-generated worlds and have dropped them in as needed/appropriate, gradually building up the star map in the course of play. But to the extent that I do so to "reward or torment" or even just intrigue the players, I think that what I'm doing is consistent with the ethos of the game even if it's a bit of a departure from its professed methods.