Maybe that is the biggest reason for some/many VCs, but given how Y-combinator started, the fact it was only investing in the Angel round, and many other facts

Maybe that is the biggest reason for some/many VCs, but given how Y-combinator started, the fact it was only investing in the Angel round, and many other facts of its history, I tend to doubt it. It could be true now, but when they started and formed this idea of Y-combinator, Paul Graham, Jessica Livingston and the others were running it a startup themselves basically as an experiment on how to get more startups to exist. I think Y-Combinator even followed this pattern with Paul recruiting the others to start the company. VCs were not in the small Angel level investment scene and Y-combinator was only investing $7000? grand in the early days. Rent for 3 months basically (oh, how rents have exploded since then). As in all complex behavior, there is not "one reason" for anything and I could have better stated it as: "I think 60% of the reason Y-combinator liked to see two or more founders is that at least those two people are willing to work with/for each other. Other people saw Y-Combinator's success and followed their example (including Y-Combinator)." It would be pretty cool if people started giving percentages to causal factors when discussing complex events. It would be a concise way to get a much more useful understanding of their opinions.