Multi-tasking takes away from cognitive focus, and makes it impossible to do deep work on a problem. Long, uninterrupted swaths of time are necessary for large tasks or for difficult problems. The concept is that multi-tasking will give us more time in the day, that somehow we can get things done quicker, and be more productive. Yet it’s amazing that most of the successful entrepreneurs I talk to prioritize getting adequate sleep each night, and focus on a single task at once. Your brain can’t split into two equally functioning wholes. The returns are diminishing with every task we try to add to our parallel workload.