The author's point meets with my own observations. Something else I observe is that a person who works on multiple projects successfully almost always has one

The author's point meets with my own observations. Something else I observe is that a person who works on multiple projects successfully almost always has one or more people who s/he can delegate tasks to. There is always someone on the project team, in my organization's case it's the software engineer, who cannot delegate. The tasks simply have to be performed by that person or the project fails. The person working on those tasks will not be able to work on as many projects as the project leader/initiator. Personally, I need 3 hours of uninterrupted time daily in order to push forward on a new application. To get maximum performance, I need two 3-hour blocks of time separated by one 2-hour block of time to do something unrelated. Another point is that the author limited his scope to work. I think everyone has multiple "projects" going on at all times. They are just not all related to work. Having a family, home, hobbies, civic involvement all necessitate working on multiple "projects" simultaneously. The people who successfully keep so many "projects" going are good at not being stressed. The author makes this point and it's a good one to reflect on.