A little while ago PUI wrote a post that explored what one's inherent capacity or potential for creative work is. One aspect she brought up is one's ability to focus for long periods of time. She mentions a collaborator (verbatim from PUI's post):
I worked with an amazing scientist on a project recently. Let's call him Co-author. He would wake up early, be in lab early, and work with intense focus until very late into the night. He didn't even seem to slow down for mealtimes. He had the ability to either be doing exactly the right thing at the right time in the right order or thinking about the next step and the experimental design while waiting for something to happen. He was highly successful in his career and could really make things happen in a short amount of time.
It strikes me that Co-author likely does not have family obligations (can stay at work every day for 12+ hours), which means he either has no family or someone else is holding the fort. I am positive different people have different capacity, but I am also completely sure that parents of young children, who are actually involved in childrearing, are not working at their full potential. And that's the way it should be, at least from the standpoint of family. When it comes to intellectually nontrivial pursuits, my most productive times used to be early mornings and evenings, but now I am up to my elbows in diapers and dishes at those times. I have almost made my peace with the fact that this is how it has to be, at least for now. Sometimes I really wish I didn't have to leave at 5:30 when I am in the middle of something exciting, but that's not an option... Another aspect is the job: like most faculty, I work well over 40 hours a week, but much of this work is not extremely intellectually challenging (administration, reports, much classroom teaching). Due to a combination of the job requirements and family obligations, I do not work at my full intellectual capacity, not even close. I do, however, work over capacity for sleep deprivation, mindless busy work, and overall aggravation.
I believe that the ability to focus is inherent only in part (see Proflike Substance's take on the issue); the other, very large part is what counts as a societal gift -- no obligations requiring you to break the focus -- and it varies with life choices. Most of us in academia simply don't have that gift any more: the ability to immerse oneself in one's intellectually challenging pursuits is a priviledge of grad students and postdocs, especially if they are unattached; I wish they would appreciate and savor it more. I wish I had appreciated and savored it more.
Regarding the necessity of focus in success I recommend "You and Your Research," by Richard Hamming (a big name in computer science). If you google it there are a bunch of links to the same transcript of his famous 1986 colloquium, most html, the link I provided is to a pdf. Hamming does advocate a fairly extreme view of the balance between work and life (hint: it's all work), but the read is provocative and invites us all to think about the quality of problems we work on. When I first read the transcript I was a bit enraged, as he does ride a high horse. But, what I chose to take from this text is the following message: Choose what you work on wisely: work only on really important problems, problems that matter. This becomes exceedingly important if you don't have unlimited time to devote to creative work.