Think you've raised enough money for your startup? Think again. You have to run through a minefield of unexpected expenses as an entrepreneur. And you never know where the big opportunity will come from. So always, always raise more money than you think you need. Mariam Naficy shares her white-knuckle experiences founding startups that survived two financial crashes — online cosmetic company Eve.com in the 90s, and founder and designer boutique Minted.com today.