I guess this depends on the stage of development for me. As a beginner the "one thing" would be getting a job. When you're beholden to someone else you lose th

I guess this depends on the stage of development for me. As a beginner the "one thing" would be getting a job. When you're beholden to someone else you lose the ability to freely cut scope whenever you're uncomfortable. Thus, I became acquainted to a "learn or fail" mentality. Eventually I got stuck in the intermediate developer quagmire - basics are too basic but advanced concepts are too advanced. I knew I needed to learn more but I didn't know what I didn't know. Not to advertise, but Hack Reactor helped me clear this hurdle really fast. I walked away with a greater understanding of how to actually comprehend documentation and assemble applications in addition to the domain-specific material that was taught. Now that I'm doing more meaningful work (though I'd hazard calling myself a "senior") my biggest growth points have usually involved having applications people actually rely on. I am my own pager-duty, so if I want comfortable weekends I need to write architecture that is capable of recovering gracefully from failures, errors that can be read by programmers or designers, etc. Answering to my users has helped me realize new ways I can meet (or exceed) their needs, areas where I was sloppy and should've handled better, and all sorts of things in-between. I'm looking forward to the next point in my career that I take a significant stride in my growth as a developer.