It really depends on the individual's overhead for context switching. Yes there is a cost, but I also think this cost is not uniform in all people. Also, nobody even on a single task, is using 100% of their capacity. So I would wager that some folks can, and do perform as well at 2 task at the same time as others do a single task.

Also remember, that somebody new to a tech might already be multitasking in the sense they are learning and doing at the same time, but somebody who has been doing the same type of work for 10+ years might not need the extra cycles for the learning part, and those could be used elsewhere.

Think about typing a comment on the internet. This entire comment took seconds to write. I am multi tasking. I am instructing my fingers to press buttons, while forming the words I wish to type, and then on top of that spelling them out. Take me when I was 8 and do the same thing and a post like this could have taken 15 minutes. While I know that there are probably 8 year olds today that could have done the same thing in less time than I can now, when I am in in my 30s.

The point being, folks can do more than one thing at once, and different folks can do more things at once as well or even better than other folks doing a single task.

We see it real well in the athletic world. Its clear some folks have bodies that allow them to run faster, or further, or jump higher, or even better eye hand coronation. To think that mental task and traits don't work the same way on a individual bases would be willfully dishonest. Some folks simply have a pertinently to spell well (I am not one of those), Some can so math with ease, and others ponder the vast theoretical realms of quantum mechanics.

People like Richard Feynman and Neil deGrasse Tyson exist, they are like top athletes in the brain game. Its clear that they have more capacity than myself, and others. So it stands to reason that some folks, and maybe many folks, can multi task better than others, and maybe that trait is what made them successful.

From my experience the talks at the water cooler are the ones that result in real change and progress. Its where the exchange of ideas happen. To think you know enough that you can sit in your box all day long and skip over hearing other peoples ideas is just elitist attitude. You won't know if you are right or wrong until its too late, and you won't be exposed to new fresh or challenging ideas without the social interactions. Hiding a way in a a box won't expose you to uncomfortable situations that will help you grow.

I work when talking though, so it was more of a joke.