For the past two years, James Quarles has run the fitness tracking app Strava, a digital community of 41 million athletes. Before that, he was a VP of Instagram, following a three-year stint as regional director of Facebook in the UK and Southern Europe. In this members-only series, Quarles lays out his key takeaways on how to launch and grow a successful business in a market that’s dominated by a handful of giants—in Strava’s case, those giants are Facebook and Instagram. Here, he explains why it’s better for a startup to be great rather than big—and makes the case for keeping your focus as narrow as possible, to let you figure out what that sweet spot of greatness might be.