In this part of the world, one encounters the unexpected event fairly commonly. It might be associated with weather, or traffic, or even ATC/FIS. It doesn't take all that long to recognise subtle signs that "something ain't right" and, at such times, my "sphincter factor" activates.
I pre-brief my expectations for each stage of the flight and am therefore alert for anything which threatens my carefully laid plans. I also try to be alert to the possibility that my expectations might be a tad too high. Being "alert" is the key, I reckon.