Kevin Ryan, the serial entrepreneur behind notable companies like Gilt Group and Business Insider, got involved in the Internet business in 1996 when he founded DoubleClick, a start-up that built ad management software for websites.

Four years later, in 2000, at the height of the tech bubble, Ryan was forced to lay off half his work force—about 1,000 people. Certainly, times were tough, but Ryan persevered, emerging from the bubble as the market leader.

"The bubble gets a lot of criticism," he said recently at the Inc. 500|5000 Conference. "I actually enjoyed the bubble quite a bit. If you're on the right side of it, it can be an incredible experience."

Ryan explains that though about 70 percent of his clients went bankrupt, they also lost about 80 percent of their competitors.

"We emerged from that with an incredibly profitable business that had a huge worldwide market share," he said.

In 2008, Google purchased DoublClick for $3.1 billion.