The thing that strikes me is some of the best ideas were not necessarily "Not X" ideas. I also don't think the contrarian thinking is as binary as "X vs Not X"

The thing that strikes me is some of the best ideas were not necessarily "Not X" ideas. I also don't think the contrarian thinking is as binary as "X vs Not X" implies. For instance, it's not like everybody in the world was thinking "a clean and concise search engine will never work" or "a social network catered towards college students will never work." Perhaps people thought "we don't need another search engine" or "we don't need another social network," but those thoughts do not necessarily make Google and Facebook "Not X" ideas. Both fixed very specific weaknesses with the then current solutions and have since evolved. Airbnb is different than Google and Facebook in that they created a market. But like I mentioned earlier, I don't think the world was thinking "I will never rent out a room in my house, if given the opportunity." More likely that thought had never crossed their mind prior to Airbnb.