The answer to OP's question doesn't seem to show up clearly in this analogy.  It seems like you stopped a little early:  After outsourcing of delivery drivers begins, the extra drivers begin throwing packages in through windows or blasting airhorns so loudly at your door that you're basically forced to open it or something, so you still get lots of deliveries despite your reluctance to deal with them and your house becomes...  fatter, so to speak.  If I'm understanding right. It seems like Poolord's answer (assuming it's correct) covers the crucial point:  Once diabetes has developed, insulin still works - but just not very well.  So if you take enough supplementary insulin as medication, that problem goes away, and you are freed up to keep on getting fatter, supposing you are foolish enough to continue overeating.  (And meanwhile, other problems arise or worsen, of course.)