This blog post was cross-posted from Quora where it was published first as an answer to a question with the same title.
Like any other startup, the 3 key ingredients (+2 bonus ones) that define success and eventually differentiate the brand:
1. The Team
If you look through their profiles there are lot of things that work for them; in no particular order: genuine, really smart, having prior experience of working together and complementary skills.
In Paul’s own words , “you don’t need a brilliant idea to start a startup around” but if we look back Y Combinator at it’s core was a pioneering effort. I would highly recommend you to read “How Y Combinator started”  which takes you through the thought process. For brevity, I would like to highlight some unique bits of the core idea in Paul’s own words:
– investors should be making more, smaller investments
– they should be funding hackers instead of suits
– they should be willing to fund younger founders
– funding startups synchronously, instead of asynchronously as it had always been done before
If you read through Paul’s essay closely you will also realize that they didn’t necessarily feel that a lot of these USPs were pioneering at the core.
Not much can be said about the execution except that it was perfect, at least to me from the time I was following them. You have to excuse me on this count because I was only able to follow them through what I have been reading about them online and through blog posts from other incubates.
Here is a small excerpt from how they started :
It’s hard for people to realize now how inconsequential YC seemed at the time. I can’t blame people who didn’t take us seriously, because we ourselves didn’t take that first summer program seriously in the very beginning.
For me what really stood out when I read how they started  was how a large part of the execution or implementation of the plan was not necessarily thinking that we are going to change the face of ‘venture funding’ or ‘incubation’ forever. It felt as if they were just doing what they believe in.
Apart from the above very obvious things which by now feel common sensical and over repeated but still people get them wrong (including me). But when it comes to being able to cerate a strong brand there are two more things that matter:
Y Combinator has created a brand of it’s own not by simply becoming a better incubator but by re-thinking form bottom-up of how an incubator should be. The timing plays an important role from the everyone’s perspective because if today there was supposed to be a right team coming together and working on the same fundamentals (idea) with brillant execution they would still remain sub-ordinate to Y Combinator as people would rightly credit Y Combinator for the seed idea.
5. Sense of Purpose
Sense of purpose to me largely is a differentiator between good and great. For every article that I have read about Y Combinator from the founders I have always felt a sense of purpose in ‘why they are doing, what they are doing’. Being able to identity a gap is simply identifying an opportunity but taking upon yourself and working towards a goal as if you were destined to work on it and no one else values it enough is purpose for me.