All of the below applies, even in a situation like this. What you’re not seeing is that it isn’t a Wild-West quick draw: it’s more like the preparation of a sniper.
There are many different types of photographers; all the way from the fully spontaneous use-whatever-falls-to-hand-and-just-hit-the-shutter-so-long-as-I-get-an-image, to the people who only photograph under 100% controlled situations – think still life in a studio, tethered. I’m somewhere in the middle, though definitely much further towards the latter end of the spectrum. The reason I’m writing this article is because during a recent workshop, I was asked by a student if I really kept all of the ‘four important things’ (and sub things) in my head and under active consideration even in a split-second instant; the answer is yes, and there’s quite a bit more on top of that – but I’ve been doing it for so long that the vast majority of the whole capture process becomes second nature.