MMM is actually an important part of the answer, and it is unfortunate that it was presented this way (death marches are deprecated for their own reasons.) The right way to think of this is to consider four people each working two hours a day on the same problem. Sustained effort and focus matter.
This is most true for tasks that are more intellectually demanding, like the development of large-scale software (which is what Brooks was writing about.) The more routine a task is, the easier it is to divide it up (though that is rarely to the benefit of the worker.)
This is most true for tasks that are more intellectually demanding, like the development of large-scale software (which is what Brooks was writing about.) The more routine a task is, the easier it is to divide it up (though that is rarely to the benefit of the worker.)