Here are my problems with retention being the star metric:<p>What if you have a customer lifetime value far higher than your acquisition costs per customer, and a very wide addressable market, but low retention rates? E.g. I acquire users for $5 each and same-day convert them to $15 profit each, and they rarely come back unless I return some of the profits back into the funnel to acquire them again.<p>You may ask - Shouldn't we assume that that growth channel will quickly collapse? -- Well, what if it doesn't? Something is very wrong with the trend of assuming that retention is everything, particularly in the case where there's a high immediate return on investment for each acquired user.<p>My second problem with retention is the time-span. Consider an ecommerce site for basic household necessities that may be accessed 20 times per year by a 100% retention user that always uses your service to his problem that your service solves. That return frequency is so low though, that if you're growing at 40%+ month over month, your retention may appear to be near zero, even though your retention is near 100%! Most of your users are new users and only a tiny percent returning, all due to your high growth rate. The compounding growth combined with the long expected time between visits just makes 100% retention look like 0%.