[crusso]

Are there any persons who can work, say, 8+ hours? I mean, really work, not be at office.

Yes. Some people can, some people can't. Some people can, but they don't really need to in order to do the job that they get paid for. Some people struggle for 9 hours a day trying to do the job that someone else can do in 2.

Mental performance varies tremendously from person to person, as does athletic performance. Can someone run 4 miles in 20 minutes without stopping? Sure. Some people can keep up that pace for a marathon (26 miles).

I wouldn't worry so much about what other people are doing. Just focus on your own performance and improve it (or don't) based upon how you feel about your productivity and its impact on your life. If enhancing it is your goal, you've taken the first step of measuring it and understanding what influences it. You could cut out distractions and see how that works for you.

For me, improving my performance has always meant synching up my work with what interests me. Sometimes that can mean changing what I'm working on - when I have that flexibility. Sometimes I have to jump-start my interest in a more boring problem by trying to mentally frame it in a way that I framed other problems that have interested me in my life.