@b0rk for me, it was inspiration, then stubbornness.
Some of Gary Bernhardt's videos inspired: https://youtu.be/ZQnyApKysg4 and a video I cannot find: "A raw view into my UNIX hackery". This post also inspired: https://adamdrake.com/command-line-tools-can-be-235x-faster-than-your-hadoop-cluster.html
Then stubbornness to solve problems from the command line when I could. This mostly leaned on search-fu, with no standout resources I can recall.
It was primarily the desire and glimpse past the horizon that spurred me to spend the time necessary to learn.
@greggyb great answer thanks