THE FEATURE THAT MADE YOUTUBE GO VIRAL HAD NOTHING TO DO WITH VIDEO
Co-founder Chad Hurley took it straight from PayPal.
At PayPal he watched people paste payment buttons onto any blog, auction, or website, and every button quietly pulled new users back. He turned that into the video embed.
Anyone could grab a clip and drop it on their blog or MySpace page, even one they didn't upload, and the whole player became an ad:
"That's how we viewed it. That was our marketing budget."
Only the small play button started the video. Click anywhere else and you landed back on YouTube.
Free distribution, paid for by everyone else's websites. Almost nobody builds for that on purpose.