This is a great essay. But, I find it odd that YC's famous "cohorts" are invented by PG. Cohorts work because startups in that batch compare against each other,

This is a great essay. But, I find it odd that YC's famous "cohorts" are invented by PG. Cohorts work because startups in that batch compare against each other, which in itself is a grading system. Getting into YC, topping the batch and raising money are inevitable symptoms of "cohort" thinking. We could argue YC uses cohorts to make startups compete for meaningful metrics instead of vanity metrics. But still, YC is based on this innate human nature to compete and get social acceptance.