What helps people get comfortable on the command line?

Okay, this is not Linux-specific, but it's about a transferable skill:

What helped me get comfortable and learn a lot of basics was setting up NetBSD. The basic install throws you into a basic command line, with no graphical interface installed and not even the internet configured. But the online guide for setting the system up is incredibly well-written and teaches you all the concepts you need to know.

After doing this, I was familiar with a larger set of terminal commands, knew how to use vi, had a bunch of practice setting up config files in CLI and even finally learned how pipes work. It's a very enjoyable experience, the guide is so good I didn't feel overwhelmed once and anything you have to look up is tied to a problem you're solving (like cursor movement in vi).

It also teaches you how NetBSD is structured. It's not Linux, but similar enough to understand a lot of how and why things are done in Linux systems