Voyeurism, mixed with a little FOMO - they had a limited release early on, just like GMail. I think a large part of it was also the digital photo and smartphon

Voyeurism, mixed with a little FOMO - they had a limited release early on, just like GMail. I think a large part of it was also the digital photo and smartphone revolution. Instagram did that a little better, but posting straight to Facebook was a little better than what... Photobucket? Personal hosting? Emails with mass CC? It just solved that problem so well for not only the big event pictures we'd traditionally throw in an album, but also adhoc slice-of-life moments. It also gave that power to businesses, humanising them in a way that hadn't been possible before, and that's where the money came in.