Insomnia might be thought of as being a bit like writers block, or any other kind of creativity a person can get blocked in.
The harder you try to sleep, the more effort your brain makes, and the more thinking you do, the more you censor yourself.
I think sleeping is actually a creative act. The more a person thinks about it, the less it will happen.
If you are worried and think you really must sleep, the pressure, and the unnecessary thinking, prevents the natural 'childlike' flow of sleep creativity happening.
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Nothing lasts but nothing is lost