It is a great question. However, I look at some of the YC funded companies(including justin.tv) and I wonder what the answer would be?

Off the top of my mind, I can think of hipmunk,1000memories etc and would like to know how the founders would answer.

It is a much more piercing question than What are users forced to do today when your product does not exist.

Justin.tv (neither an online streaming live show of some guy's life, nor a streaming platform for live video) didn't exist before we were funded, fyibtw.

Justin, I totally agree that what you did with Justin.tv was novel and didn't exist before. However, how would you have answered Why doesn't it already exist?

Ah, sorry, reading comprehension fail.

Why didn't the platform exist pre-Justin.tv?

1) Bandwidth prices were much higher in 2007, and have plummeted in the past few years, making the economics more attractive.

2) There were no good, stable streaming servers commercially available. Flash streaming in FMS 2 was a joke (it would fail constantly) in 2007. Fast forward a little while and you had Red5, FMS 3, and Wowza all with video streaming to a Flash client.

3) Video advertising market grew significantly starting around 2007, providing a monetization model.

Hope that explains it!

Could you really have provided these answers back when you were at the interview stage of getting funding? These all seem accurate in hindsight, but the kind of things you never would have known up front...

Edit: This isn't meant to be critical; I'm just curious how you would have answered back in a 2k7 interview?

Doubtful. We didn't even have the idea of the platform when we came up with Justin.tv. Our pitch was more along the lines of "Here's something we're passionate about that is cool" -- PG believes in funding people and believed in funding us. We figured the rest out as we went along.

Definitely. And it will make you think about possible barriers to entry if you were to create the idea.