Before Rust, I'd reached the personal conclusion that large-scale thread-safe software was almost impossible -- certainly it required the highest levels of software engineering. Multi-process code was a much more reasonable option for mere mortals.

Rust on the other hand solves that. There is code you can't write easily in Rust, but just yesterday I took a rust iteration, changed 'iter()' to 'par_iter()', and given it compiled I had high confidence it was going to work (which it did).