"Multi-Tasking" Is Destroying Our Brain"

After completing Project Management training in 2015, I got to thinking, multitasking is a requirement of operations management, that venerable branch of business studies that deals with how factories, supply chains, and research projects are run.  The "critical path method" algorithm involves listing all tasks or jobs required to complete a project, the duration of each, and any dependencies (tasks that must be completed before another is undertaken; for example, in construction, a foundation must be poured before sill boards can be laid).  Based on dependencies and job-time lengths, a critical path is found through the process that defines the minimum total time to completion.  All other tasks, for which there is "slack" (extra time either before or after the task), are fit around the critical path so as not to lengthen total job time.
Everything that can be is executed in parallel.  The actual tasks are typically done by different people.  The number of parallel job streams defines the labor requirement (how many people to put on the job). Sounds sensible, this confirmed a level of consciousness for me, you need more than one person to complete a project.
Some jobs can and have to be run in parallel, but one person should probably not be doing more than one thing literally at the same time, or quality suffers.  Rapid task switching, which may look like multitasking, is common and required for many types of activity.  Multitask where you can, task switch when you have to, and focus on the job at hand as much as possible for the best results.
Nonetheless, the term multitasking originally comes out of the computer science literature and refers to independent computing threads run at the same time.
We really are not very good at multitasking and it can have some consequences, actually hurting our productivity because of the time lost making even fast switches. I've watched individuals trying to multitask be forced to retrace their steps or redo something. 
John Medina, the author of "Brain Rules," also points out that the brain cannot multi-task when we are doing things that require our attention or effort. He argues that we take 50 percent longer to accomplish a task and make up to 50 percent more errors. Certainly, we can do several things at once if they do not require much attention, like exercising while listening to music or eating while watching a movie; it's those things that require more attention or involve people that create multi-tasking trouble.
It's suggested that the cost of interruptions to American workers and the economy in terms of lost productivity and profitability is staggering (more than $650 billion a year) due to Multi-tasking.

So, understand that multi-tasking with tasks that require our attention and effort is not productive and studies show for multitasking is actually a bad thing for most white collar professionals. "[Multitasking] shrinks our brains. When you overload your brain trying to get it to task switch, you shrink the gray matter in your brain.
Single-tasking is working with our brains the way they were created. It means keeping your brain and body in the same place and focused on one thing at a time.
You can get more done in the course of the day if at any given moment you're fully and intensely immersed in the task at hand."

The solution to multitasking is, unsurprisingly, single-tasking. You focus 100% of your attention on a single cognitive task and pour your energy into it from start to finish. Instead of splitting up your limited mental resources, you concentrate on one thing at a time.