I wasn't arguing that they did wrong at all by trying (although I actually hated refer.ly but not the founders from the beginning, and told them this; mostly because CPA/affiliates is a scam-filled shithole, even if sometimes profitable, and the whole lie down with dogs/fleas thing).

But sticking with something past the point where it's clearly failed is where the opportunity cost argument comes in. If they'd stuck with refer.ly for an extra year after it was clearly doomed just because they had nothing better to do, that would be wasting opportunity. Pivoting into something more interesting, either with a new business or the same corporation, is the best thing to do.

A team which could easily do a bunch of other cool stuff clearly has higher inherent opportunity cost than a team fresh out of college without a lot of ideas. This is kind of why medical startups often suck, because you do need to involve MDs, and MDs have a $250k+/yr job practicing medicine (with high social status as well) as their best alternative -- so anything short of a potential big win isn't worth it for them.