I had this cute story quietly bouncing  around the back of my head until I heard that WardAndKent work better together than separately, and noticed similar effects with other experts on projects.  Actually there are two stories I heard, both paraphrased below because I don't have perfect memory.

"I saw an ad for 'the tallest corn in the world', so I ordered it.  Sure enough, that stalk of corn grew so tall I couldn't believe it.  But I was horribly disappointed when the ear of corn grew.  It was tiny :-(        Later, I learned that corn gives its biggest yields when grown in bunches (no doubt there is a reason).  It seems corn needs other corn nearby to grow properly.  My solitary stalk of corn was tall, but did not give much yield."

Other story was about horses, I don't have the numbers correct, I am sure, please forgive that, but they are close...

"In hauling contests, one horse can haul up to 1200 pounds, but two together can haul 3000 pounds."

''Also consider that when geese fly in formation, most of them can fly with half the effort.''

I think of the CornFieldEffect when I see designers feeding off each other's ideas to create a better design.  I use this as a basis for the DayCare pattern. --AlistairCockburn

See also BasketballMetaphor for another angle.
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Wouldn't Synergy describe this?  Or does Synergy have a connotation of differing qualities?  --PeteHardie

''Synergy does describe this, but only by those who can stand to hear the word.  To many techies, the word 'synergy' sounds like content-free corporate fast talk.  --RobMandeville''

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''Sometimes "1 + 1 = 3".''