I like when candidates talk about a missed opportunity, such as missing out on securing an account. Describe the situation and explain what was at stake. Tell what needed to happen to get the business. Explain what kept you from securing that business. Did you not have the resources? Did you fail to speak with the right people? Maybe you had to make a strategic decision to allocate your time and resources elsewhere. Most importantly, how has this changed the way you do things? Did you learn something valuable that makes you better now than before?