The Silicon Valley dream is to build a tech startup that is such a unique idea it alters the commercial universe and turns its founders into billionaires. Participating in the Valley’s most famed startup factory, Y Combinator, is often part of that dream. Airbnb, Coinbase, and Stripe all got started there. Yet, a deep dive into the data from all of the nearly 5,000 companies YC has backed to date reveals a surprising truth: YC startups don’t have to be unique. Far from it. YC commonly accepts st...