What skill made the biggest difference after you got your first pentesting role?

I've been looking at what separates someone who can perform a pentest from someone who can consistently deliver useful work. Knowing the tools seems important early on, but the work also involves understanding applications, validating findings, collecting solid evidence, and writing reports that developers can actually act on.

That makes me think the biggest career gains may come from improving the work around the testing itself, rather than simply adding more tools to the toolbox.

For people who've worked in pentesting or AppSec for a few years, which skill made the biggest difference after you got your first role?