What does it mean that single-tasking outperforms multitasking?

Doing one thing at a time produces better results faster than switching between tasks.

Example: A product manager at a mid-size software company believed he was exceptionally good at multitasking. He kept Slack open on one monitor, a product requirements document on another, and his email in a third window. During any given hour he would respond to three Slack threads, edit two paragraphs of the requirements doc, scan a dozen emails, and glance at a dashboard. He felt productive — busy, responsive, always on top of things. Then his VP asked him to produce a competitive analysis by Friday. It required sustained thinking: comparing pricing models, synthesizing customer interviews, and constructing a strategic argument. He sat down Monday morning with every intention of writing it. By Friday, the document had 400 words. Not because the analysis was difficult. Because every time he entered the document, a Slack notification pulled him out within eight minutes. Each return to the document cost him ten to fifteen minutes of re-reading what he had already written, re-establishing his argument, and re-entering the analytical frame. He was not writing a competitive analysis. He was repeatedly starting to write a competitive analysis. The following Monday, he tried something different. He closed Slack, silenced notifications, and worked on the analysis for ninety uninterrupted minutes. He produced 2,200 words of coherent strategic argument — more than five times what the previous week had yielded in five days of fragmented effort. The analysis was sharper, the reasoning more connected, and the conclusions more defensible. Nothing about his intelligence or skill had changed. The only variable was whether he gave the task his full attention or divided it across five simultaneous streams.

Try this: Run a single-tasking experiment over the next three working days. Choose one meaningful task each day — something that requires genuine thought, not mechanical execution. On Day 1, work on the task the way you normally would: notifications on, tabs open, responding to messages as they arrive. Track two things: total elapsed time from start to a finished output, and how many times you switched away from the task. On Day 2, choose an equivalent task. This time, close every application except the one you need. Silence all notifications. Set a timer for 45 minutes and work on nothing else until it rings. Track the same two metrics. On Day 3, repeat the Day 2 protocol but extend to 60 minutes. After three days, compare: total time to completion, number of interruptions, and — critically — your subjective sense of the quality of the output. Most people find the single-tasking sessions produce better work in less total time, often dramatically so. Write down the specific numbers. This is not an opinion exercise. It is a measurement exercise.