Mike Hill discusses How TDD and Pairing Increase Production, and he is right.
Today, two of us have been working, and have made progress, but the reality of the situation is that we've only commented out a few lines of code and run the debugger. Neither of us have worked in this code before, and there are no existing tests. Just finding our way is work. Real work requiring attention and sifting through many facts for the few that give us a clue as to what is not really working and why. We're spending the day (so far) reverse-engineering older code and trying to understand how (and whether) to make our change.
Programming is largely about thinking, planning, scheming, and not making mistakes. I do those much better with a partner.