Why December is decided in September
The tables, rooms and aircraft worth having in December are committed by early autumn. What that means if you are planning now.
By the time most people begin thinking about December, the interesting parts of it are already gone. Not sold out in the way a website reports sold out. Committed, quietly, weeks earlier, to people who asked in September.
This is the least intuitive thing about the season. Demand is obvious and everyone can see it coming, so the assumption is that supply responds in kind: that a room facing a hard month will hold something back and release it late, at a price. The opposite happens. Scarcity makes a room more conservative, not less. It commits its December to the names it already has, because those are the bookings that will not evaporate in the second week.
A restaurant's December is largely spoken for by the first week of October. Not through a booking system, but through a list of regulars, house accounts and standing arrangements that never reaches a public calendar. What surfaces online in November is the remainder, and it looks like the whole picture only because the rest was never visible.
Hotels do the same thing with their better rooms. The suite you want for the week between Christmas and New Year is not sitting in general inventory in December waiting to be found. It was allocated in the autumn, and the rate you are quoted in November is what is left after that.
Private aviation is the most exposed of the three, because the binding constraint is not aircraft. It is crew. Duty limits do not relax for the holidays, and an operator with a finite roster works out in October roughly what its last fortnight of December can physically look like. It then spends that capacity on the clients who flew all year rather than the ones calling for the first time on the nineteenth.
Anything made by hand runs on the same clock for a duller reason. Lead time. A commission placed in late November is a commission for February, and no amount of goodwill compresses a workshop.
The practical version is short, and it does not require you to have decided anything yet. Fix the dates that matter while they are still abstract: the nights you want to be somewhere, the days you would rather travel, roughly how many of you there are. The detail can come later. What cannot come later is being on the list before the list closes.
None of this is urgency for its own sake, and it is not an argument for booking everything now. December simply runs on a longer clock than the month it occupies. The people who get the version of it they actually wanted are rarely the ones who planned hardest in December. They are the ones who asked in September.