There's one missing point on this post that I believe is important. I don't blame them for not putting on there either though since it's a bit intangible:

YC really encourages commitment. Commitment to your idea and co-founders. That commitment inspires a lot of motivation to do a lot with little in a very small amount of time.

You go from a rag tag group working on weekends and evenings due to school or your day job to a competitive, hungry machine ready to usurp your market leader.

The effect of the peer pressure amongst your batch mates continuously making progress each week is substantial.

YMMV - it worked for us at Mixpanel.