I haven't gotten to pair-program much, but I'd like to.  Pair-programming is where two developers work on a single screen with a single keyboard.  The typos, bugs, distractions, rabbit-trails, poor writing tendencies of developing solo are reduced by two people working together. One of the benefits of pair-programming is there is someone there to say, "hey, what you just did looks right, but that's actually going to screw up something we did on Monday". And in that small sense, developing test-first or with behavior driven development (I use Cucumber to do BDD)  you "pair program" with your past self who wrote a test-suite on Monday before implementing a feature.  Now you can hit a button, and run all your previous tests and ask your past self, "Did I break anything that I've already completed?" and your test suite will let you know.