Recently I read Deep Work by Calvin Newport, where it talks about importance of work done with high degree of concentration. In another post he talks about importance of hard focus. It's an amazing book, read it! It got me thinking about the role of focus in my life.
I remember how in high school I was better than some of my peers, even though I spent less time studying. I remember also being better in better in Muay Thai than some of my peers that started nearly at the same time as I did. I don't believe I'm especially intelligent. Neither I do believe that I have some kind of a talent for martial arts (I generally don't believe in talent, but rather hard work). I believe my results came from my efforts in focusing. Whenever I study, I make sure that I don't have distractions, and the material I'm studying is the only thing I'm thinking about. Whenever I box, I only concentrate on my techniques and my opponent (in my later post I'll talk about how focusing is easier in a full-contact martial art, since you're getting beaten!).
Overall, I believe your productive work is the time you spend multiplied by depth of focus and concentration. Spending time on something without a focus is indeed a waste of time.