If you want something done, ask a busy person to do it

Someone at the American Dialect Society (Goggle's web version does not give a name but I'll try and post the details some other time) gave the origins of the saying which seems to go back to the late 1800's at least.
And how true it is .... definitely appropriate for me.
I think the reason that a busy person can take on more has something to do with flow .... when we have the momentum and energy associated with action then we can easily accomodate more.
When we do less than is optimal we have to put in the effort needed to "prime the pump" and that can consume greater energy than the activity itself.
It is like the activation energy for a chemical reaction - once started, the reaction will continue .... but it make take some "heat" to get things going.