A children's book charting the adventures of a little black fish and a Bangladeshi economist's treatise on social business seem like odd bedside reading for a budding internet entrepreneur.

But for Rob Kalin, the 27-year-old founder of Etsy, an online marketplace for handmade goods, the two books - Leo Lionni's 1973 children's classic Swimmy and Muhammad Yunus's Creating a World Without Poverty - have provided valuable lessons for running a rapidly growing online start-up.