In my experience, I've seen 3 kinds of jobs that demand engineers who can solve "hard" problems: 1. Obviously hard, and needs no explanation e.g. self-driving

In my experience, I've seen 3 kinds of jobs that demand engineers who can solve "hard" problems: 1. Obviously hard, and needs no explanation e.g. self-driving cars. 2. Basic problems done at ridiculous scale. Quickly matching keywords to web pages is not a hard problem; quickly matching keywords to every web page on the internet is a hard problem. 3. The problem is that (forgivably or not, depending on circumstances) we have no idea what we're trying to do.