I have been a solo founder my whole life and have managed to start several businesses without the need for outside funding. Yet, when I decided to explore my options and try to join an incubator for my next venture, I quickly realized that being a solo founder is an automatic rejection.
Why is that the case and what is the methodology behind such a thing?
The assumption is that a single person, however smart, is unlikely to have the set of skills necessary to get a business off the ground. Also, you often hear getting a co-founder is a proof that you were able to convince at least one other person about how great your idea is.
The first reason is just practical. In early stages there are too many things to do on your own, and even if you have the variety of skill (technical, market/niche expertise, business, sales, writing, etc) you need a) a sounding board for your ideas b) support of every kind - emotional, financial, etc. The statistics for failing single founders are brutal.
Ideal co-founders have complimentary (!) skills with minimal overlap, but are hopefully like-minded individuals who can build a strong partnership.
YCombinator has funded solo founders. But these have been outliers. The bulk has always been more than one founder.
Here's a list of startups they've funded that had just a single founder at the time of the interview:
W06 - Charles Forman (iminlikewithyou/OMGPOP)
W08 - Altay Guvench (MightyQuiz)
W09 - Sam Odio (Divvyshot)
W09 - Gabor Cselle (reMail)
S10 - Euwyn Poon (Opzi)
S10 - Eric Dementhon (Padmapper)
S10 - Ray Grieselhuber (GinzaMetrics)
W11 - Chris Chen (like.fm)
S12 - Kirill Zubovsky (Scoutzie)
S12 - Gabe Ragland (imgfave)
S12 - Brian Armstong (Coinbase)
S12 - Bryan Beshore (Keychain Logistics)
W13 - Nikhil Nirmel (Lawdingo)
I've heard that usually if Paul and the team really like you, they try to match you up with a co-founder that would provide skills you might lack.
Parse's Ilya Sukhar applied to YC as a solo founder as well.