>The problem with your scenario is that it highlights interruptions. I still manage to get things done - in spite of interruptions.
>
>And of course, you necessarily assume that something necessarily has full-time requirements...

Well in THIS case it surely is better to assume that full time is needed until PROVEN otherwise. And "proven" is a key word here.
Proving that one can save some money by making an activity part time instead of full time is never hard to do at all. Proving that all a job needs is part time attention - there will be NO loss of quality/service/whatever - is another thing altogether.

I think it can be safely concluded that Mr. Green was handicapped in his efforts to market VFP by being spread very thinly across several endeavours.