Anyone who has lain awake at night trying to think something through will recognise this little poem. The speaker is in bed, surrounded by stillness, and starts to think about the world. Big thoughts, it seems, but we never find out what they are. The line "I think...................." trails off into a long string of dots, and then comes the blunt "Too late. I'm asleep."
The joke, gently, is that sleep arrives before the thinking can. The repeated words "still," "quiet," and "calm" build a soft, lulling rhythm, almost like someone drifting off, and the repetition of that group of words makes the speaker's second attempt feel like a loop. The dots stretch out the moment of slipping away. The speaker doesn't seem upset about losing the thought. The mood is peaceful and a little amused, as if falling asleep is the one thing that wins over even the world's biggest questions.