Ask HN: How do you focus on work for long periods of time?

I've used Adderall (not ADHD diagnosed) a couple of times, and it helps a significant amount. However, I know it can't be the real solution - my problem is concretely that anytime I work on something, I can't work on it for long amounts of time - every 15 minutes, I will either visit HN, Reddit, some game, or have to get up and physically leave the desk. I can't bring myself to work on things for extended periods of time. How do you guys do it?