Go pull a bunch of grass, and put it in a pile. You now have a working pillow.

That doesn't sound comfortable. I'd probably rather sleep on my arm than a pile of grass...

Im sure if you spent your whole life sleeping on the ground youd work something out to make it more comfortable

But that was the point... why don't gorillas make pillows then? My contention was that making a pillow is actually difficult. I wouldn't be surprised if pillows were seldom used by early humans.

This is a failure of your imagination, not the grass.

It can be actually comfortable.

You (most likely) have two comfortable potential pillows distal to your elbows...

(I don't use any of these positions, but I most commonly nap on a heated wooden floor in an insect-free environment. Oddly enough, I also support my temple on the dorsal surface of a wrist; it had never occurred to me that in addition to comfort, it keeps both ears free?)