This can definitely be learned in a methodical way, this is very common in the military, for instance. Of course, this will usually not work when you are wide a

This can definitely be learned in a methodical way, this is very common in the military, for instance. Of course, this will usually not work when you are wide awake and not sleepy at all, but in that case it is also not needed. So you are not wrong: this is for times when you simply cannot have a normal sleep schedule, for instance during a military operation or while doing a multi-day shift at the hospital, where you are practically always sleep-deprived. In the military, this is methodically trained specifically for these situations, in a civilian setting it will often simply develop naturally, out of necessity.