So we have scales that allow us to divide up people into people who multitask all the time and people who rarely do, and the differences are remarkable. People who multitask all the time can't filter out irrelevancy. They can't manage a working memory. They're chronically distracted. They initiate much larger parts of their brains that are irrelevant to the task at hand . . . they're pretty much mental wrecks.
- Clifford Nass, Stanford communications professor, quoted in Deep Work by Cal Newport