A few writers and thinkers seem to have caught onto the same thing. I believe I could find a host of other thinkers, such as William James and Victor Frankl, who would agree with them:
"When one is busy and absorbed in one's work, the very absorption affords great delight." Seneca
"To fill the hour--that is happiness." Emerson
"Flow" has been called an "optimal experience." It's a state of "effortless concentration so deep that [the persons in the flow] lose their sense of time, of themselves, of their problems." There are two forms of effort: "concentration on the task and the deliberate control of attention." When you're in the flow, the deliberate control of attention comes naturally: it just occurs without trying. The "resources" that would be spent on trying to control your attention can, instead, be spent on the task at hand, thereby making you more effective when dealing with the task at hand. Adapted from Daniel Kahneman, Thinking, Fast and Slow
"If most of the time you're not particularly concerned about whether what you're doing is work or play, or even whether you're happy or not, you know you're living the focused life." Wilfred Gallagher, Rapt
Problem is, it's a bit difficult to get into the flow, and once you're into it, the Attention Pests (i.e., other people) are more inclined than not to interfere with it. I have a job that affords many opportunities to get into the flow, which is one reason I really like my job. But I have an office that provides many more interruptions to the flow, which is why, although I otherwise find my office an amenable place, I don't like working in the office.
My son, Alex, told me that a rule of etiquette has emerged on college campuses, at least at the University of Michigan, where people are supposed to be immersed in the flow frequently: don't bother someone wearing thick headphones. If a person is merely wearing the "ear buds," then it's fine to talk with him. But if the person has the thick headphones on, that means he doesn't want to be bothered (for whatever reason; maybe he's in a bad mood or maybe he's trying to get into the scholarly flow) and it's rude to do so.
I think that's a great development. We've kind of adopted it as a rule around my house, and it's working fairly well. Now I just wish I could find a way to implement in society at large.