Ask HN: What's a surprisingly useful tech skill that's underrated today?

We often talk about mastering popular languages, frameworks, and AI tools. But what about the less-hyped skills that quietly make you 10x more effective?

For example:

Knowing how to write a custom shell script that replaces a SaaS tool

Building internal tools with no-code + cron + GitHub Actions

Understanding how to optimize a slow SQL query line-by-line

Crafting a bash one-liner that saves you hours every week

Using the command line like a superpower

I'm curious: What are the most underrated but highly valuable tech skills you've learned that more people should know about?

Would love to hear stories, examples, or even niche tools you swear by. Bonus points if it’s something you only discovered by accident or necessity, not through a tutorial.