I've mentioned this in another post. I'm a CPSC University of Calgary alum. James Gosling (Founder of Java) is also an alum. A bunch of my profs went to school with him back in the 70s and the stories they told about him. Well he was a legend. One day he came to do a talk when I was in undergrad. He told us that he applied to every major CPSC school for his PhD and was rejected EVERYWHERE except for Carnegie Mellon. As he was about to walk across the stage to be awarded his degree there, they pulled him aside and told him that each year they randomly select one person that they initially rejected and accepted that person, and that he was the first one that ever graduated. Even James needed luck. I would love to see the same experiment done with YC. IT would be one hell of an experiment.

I can't find a source for LightSail having been rejected from YC, the linked reference is just a crunchbase entry that doesn't mention YC as investors.

I'd be super interested to know more about this, since LightSail seems like exactly the type of company (and founder) that YC says it wants to fund: Working in a RFS domain (energy), massive potential upside, and founder with considerable domain expertise.