It is useful to know what one is good at, but also what one is bad at.
The example I am thinking of is multitasking, doing and thinking about several things at once. The first clear evidence of my inability to do it well appeared decades ago in the context of my medieval hobby, which included combat with medieval weapons done as a sport. I was much worse at melee combat—one group of fighters against another—than at single combat. In single combat I only had to focus on the opponent I was fighting. In melee, I had to be, or at least should have been, simultaneously keeping track of everyone else near me. And I wasn't.
The same problem showed up much later in the context of World of Warcraft. Group combat there, a raid with a group of from five to forty people, requires the player to keep track of what he is doing, what other people in the group are saying—in the form of typed messages on the screen—and other things going on around him. I focused on what I was doing and frequently missed important things other people were saying. Interestingly enough, that was less of a problem if the group was using software that permitted voice communication, so that one kind of information was coming in mostly through my ears, another through my eyes.
It is not just that paying attention to multiple things is hard. My daughter, playing the same game, can not only pay attention to everything in the game, she can also conduct one or two independent conversations, in typed text, while doing so. Pretty clearly, it is a real difference in abilities, whether innate or learned I do not know.
Thinking about it, it occurred to me that I had observed the same pattern in an entirely different context, the difference between how I think and how Richard Epstein, a friend and past colleague, thinks. I usually describe the difference as my thinking in series, Richard in parallel. It shows up when he is sketching the argument for some conclusion.
A implies B. B implies C. C ...
At which point I demonstrate that B doesn't really imply C, that there is a hole in the argument. That is no problem for Richard, who promptly points out that A also implies B', a somewhat different proposition than B, which implies C', from which he can eventually work his way back to D, or perhaps E or F, and so to the conclusion that the original line of argument was intended to establish. Pretty clearly, he is running a network of multiple lines of argument in his head and only has to find some set of links in the network that gets him where he is going. I am focusing on running a single line of argument. Hence parallel vs series.