Some people can. In the bonus material for the LOTR extended edition, Elijah Wood talks about how he can fall asleep virtually on command, and this comes in very handy in film acting, where you often have many periods of waiting in between being able to work. Other cast corroborate this, commenting on seeing him sleeping frequently.

I basically can. If I lay down I can daydream into hynagogic imagery and then it’s sleep from there. I used to be an Insomanic but the last few years have been pretty easy.

Sleep now is a lot more difficult than sleep 100 years ago.

Light matters. Blue light from computer screens has been tied to sleep issues. The theory is that it mimics certain bandwidths of sunlight that our eyes are primed to read as “daytime, get up and start moving.”

Hydration and food matters. You need to be in a good state but shouldn’t consume much right before bed.

Exercise matters. A lot of people have trouble sleeping if they move around a lot before bed. Since we have electric lights and can stay up very late doing stuff, it’s hard for your body to know it’s time to start winding down.

Best solution I’ve found: no caffeine after noon, consistent bed schedule (both going to sleep and waking up), black out curtains and/or sleep mask, earplugs/earbuds/brown noise track, and stop using screens an hour or two before bedtime.

Years I I remember reading something about it as an evolutionary necessity. I have no reference now. Anyway it says that having in a tribe people accustomed to fall asleep at different times and in different condition allowed to have always at least one person on a watch for dangers coming from the outside. This does nor explain why people struggle to fall asleep for long hours, but at least it gives a partial explanation.

I’d love to be able to sleep on command.

Usually I need to take a melatonin pill after tossing and turning before I get some sleep.