What tech skill gave you the biggest boost in your career?

Having worked with many different environments/programming languages/tools

Git

Maybe not a tech skill, but public speaking. I forced myself to give talks at code camps after recognizing it was a glaring weakness of mine. Was hired by Microsoft as a cloud evangelist as a result. There was also a lot of interest from local companies who sponsor those sorts of events.

Knowing how to communicate both verbally and written, persuasion, talk to “the business”, navigate corporate politics, building networks internally and externally.

I got tired of being the geek that everyone ignored over a decade ago.

Pattern recognition. I don't mean the ability to do regular expressions. I mean the ability to recognize patterns in software development, organizations, and trends in the industry. It helps recognize when you've seen something similar before and know a good approach to dealing with it. This would include design patterns (like Gang of Four), integration patterns, architecture patterns, etc. There are a lot of problems out there that have stable, known solutions to them.

Writing.