In its early years, Twitter was leaving 70,000 signups a day on the table, although it didn’t know it at the time. Three of the company’s employees eventually uncovered the issue, leading to hundreds of millions of dollars of valuation. This is one of the anecdotes that kicked off the concept of “growth hacking” — the idea that a talented person focused religiously on growth, with the right analytical skills to tightly track that growth, can scale a company very quickly. Andy Johns, now Head of Growth at hot financial services company Wealthfront, but formerly one of the three-person team at Twitter who uncovered the company’s overlooked opportunity), defined the role for me...