–Premal Shah, President of Kiva, the microfinance website that connects citizen lenders with entrepreneurs around the world. I interviewed Shah for Fortune‘s list of 40 under 40 in the current issue–he’s No. 31 with Kiva CEO Matt Flannery.

While Shah’s passion for microfinace drives him, it can also be a stumbling block. “Like a lot of entrepreneurs, and especially social entrepreneurs, I get pretty fired up and attached to my own viewpoints. At times when I have disagreed with someone, when the stakes are high, I can take it personally and it’s added distance between me and the person,” he says.

For more of the 40 under 40 on their mistakes, regrets and pitfalls, click here. –Jessica Shambora