Ask HN: What things have richly rewarded the time invested in mastering them?
A few things.
- A habit of reading: Took a while but, whenever I am traveling, I am reading stuff. Books, articles you name it. But strictly no social media. BTW, Pocket is a great app for this. 
- Learning vim: Writing code faster has really paid off. I have reached a point where I don't remember the vim key bindings. But my hand does. So things are pretty fast.
- Learning emacs org mode: All the writing and planning activities have become much simpler. Highly recommend it.