Fewer Tasks for Productivity

As fewer tasks you assign to a person or to a team the more effectiveness raises. This is according to some consultants for office effectiveness. They describe this as a paradox of the productivity. I don’t understand why they call this a paradox? It is absolutely obvious to me and I think to anyone else also, that the less things you have to worry about the better your brain functions. There is no need for some highly paid consultant to come and say this to me. There is no need to write profound articles on this subject. Sometimes I wonder why and how such “consultants” exist.