It was supposed to bring massive concurrency to Python. But as with any async implantation in any language it is too easy to deadlock the entire system. Did you forgot to sprinkle enough `await`? Your code is blocked somewhere, good luck hunting for it.
In contrast preemptive green threads are too easy. Be it IO or CPU load all threads will get their slice of CPU time. Nothing is blocked so you can debug your logic errors instead of deadlocks everywhere.
Async works in JS so well because the entire language is designed for it, instead of async being just bolted on. You can't even run plain `sleep` to block, you need setTimeout.
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