[clux]

Asynchronicity isn't an optimization, it's a simplification. Blocking code and threads are hard to reason about, but callbacks are simple. You still have to deal with errors in a synchronous world, and an evented system allows you to deal with branching event possibilities sanely.

[ef4]

Yes, pre-emptive blocking threads are hard to reason about.

But cooperative blocking threads are just as easy to reason about as node's callbacks, while being significantly easier to structure and make fault-tolerant.