This may be too direct question to ask, but I will anyway to have some points of reference... 1. What do you - at YCombinator consider to be your best example

This may be too direct question to ask, but I will anyway to have some points of reference... 1. What do you - at YCombinator consider to be your best example of a successful start-up? If you can name that company, that would be awesome and appreciated. 2. On the other hand, what do you consider to be a flat out failure? An example of an idea that totally did not work? If you could name this venture, it would be appreciated too.