David Karp was 20 years old in 2007, when he created a wondrously visual alternative to Wordpress and Blogger. Around the same time, Garance Dore was a style-conscious French gal who learned some html so she could beautify her personal blog. Neither will admit that they had a grand plan at the time.

But they did share one little trait: The ruthless ability to say "no" to what everyone else was thinking at the moment.

In the early days of Tumblr, the site's abilities were decidedly minimal. There was just posting--there were no comments, messaging, or re-posting. And the site's users were clamoring for comments. "All the other guys did comments; they were really ubiquitous, but they never really turned into something that exciting," Karp, Tumblr's founder and chief executive, said onstage at the Fast Company Innovation Festival in Manhattan on Wednesday.

"As we started to think about it, we realized comments were always second-place citizens," he said. "We said, 'what if we gave everybody an equal soapbox?'" Tumblr's small staff said no to the idea of comments, and wrote their own original code to allow individuals to repost Tumblr posts they like. "That's where the 'reblog button' came from."

He says it was a defining aspect of Tumblr, and fostered growth of the connective tissue between publishers on the site. Moreover, it allowed Tumblr to evolve beyond a simple web-posting tool, and gain something of a personality as a brand.

Within years, Tumblr was also saying "no" to advertising, and "no" to a "buy" button. And it kept a firm hold on its creative soul.

Similarly, blogger Garance Dore, who appeared in the on-stage discussion with Karp, said her creation of a personal blog was part of a "rebellion from the system" back in the mid-2000s.

She said early on, she struggled with whether to use advertising on the site--something other bloggers were beginning to do indiscriminately. The answer she came to was not to say "no" to it just once--but to have to say it over and over again along the way. She is selective about which campaigns the site accepts. "We say no all the time," Dore says. "We just said no to an advertising campaign for a perfume that I didn't think smelled so good."

For her, creativity takes time and space. And she wants the business that the blog has spurred to reflect that spirit--and not grow too big for it. She says: "My choice has also been to stay at a size that allows us to say no to things, not to become a big machine."