Needs to be both. When I was young I directed intense focus on a new thing as soon as I got bored, but went deep into it and sometimes beyond (i.e. tetris long past the point I was learning anything). As older, I get faster at getting to 80% of it in 20% of the time and only stick around to get more information if it is directly related to a goal or of particular interest. I like that in a new fresh field there is so much to gain in so little time, and am not much into repetitive or tedious motions. That said, getting all the way to mastery in a few holistic areas is invaluable, as the hard to reach lessons are often widely applicable.