A common client objection to pair programming is that the project isn’t big enough for two people. The assumption being that more programmers means more work accomplished (at greater cost).
It occurred to me today that perhaps the best response to this is to make the comparison to the pilot/copilot system in aviation. It’s not that the extra pilot gets you to the destination any faster. It’s that the chances of crashing and burning along the way are drastically reduced.
Of course, in software, the presence of a pair partner generally does accelerate progress. But that’s not the purpose, it’s just a bonus.