A Roman got there first
Publilius Syrus was a Syrian slave who became a writer of one-line maxims in first-century BC Rome, and “to do two things at once is to do neither” predates every modern study of task-switching by roughly two thousand years. It is worth sitting with that. The distraction problem is usually discussed as though phones invented it. What phones did was make an old and well-documented human weakness cheaper to indulge.
The subject is old and the urgency is new
The lines here run from a Publilius Syrus translation to 2007, and the distribution is lopsided towards the recent end in a way most rooms are not. Attention has always been finite; what changed is that it became something other people are actively buying. Everything before about 1990 in this room treats concentration as a personal discipline. Everything after treats it as a resource under attack — which is a different claim, and the room is where the two meet.
What is the best quote about focus?
Alexander Graham Bell’s, because it explains the mechanism rather than just urging you on: the sun’s rays do not burn until brought to a focus. The energy is not the variable — the gathering is.
Who said “to do two things at once is to do neither”?
Publilius Syrus, a Roman writer of the first century BC, in his collection of Sentences. He was brought to Italy as a slave, freed for his wit, and became famous for exactly this kind of one-line maxim.