I have seen a lot of 3-founder teams fail due to founder breakup. It was pointed out to me that 3-founder teams may be the most unstable because it only takes 2 founders to agree to make a decision. Often this pattern recurs until one person feels left out and leaves.

I think one of the biggest mistakes that startups make is not getting on the same page from day one, and letting small differences become large ones. This applies equally to any sized team, but may get exacerbated as your team increases in size, and there may be a huge jump in this problem as you get to size 3.

Then again, every team size comes with its own set of issues. I wouldn't say 1 is too few, 3 is too many, and 2 is just right. I'd take this article more as, 'the perils of a 3-person startup.'