Although the previously linked Foundation post with Tony Hsieh was interesting, this episode of Foundation with Kevin Systrom spoke to me more. This episode is from back when Instagram had 'just' 15 million users, and he's giving a great insight into what was happening in the early days of IG, about his time with Odeo, how he went from a marketing job at Google and where he put the focus in his startup.
Where Hsieh focused mainly on company culture, an intrinsic part of Zappos' identity and customer experience, Systrom meticulously talked about the product. Not to add a bunch of random features but have a few and do those extremely well. Look at the top 3 problems people have and solve those. Identify what people love about your app and make those infinitely better through iteration and testing. His vision on private beta's, feedback and being scared are inspirational. If you have 48 minutes to spare, spend them on this episode.