The key is staying diversified and not becoming too dependent on a big commercial account. My friend made that mistake, and had the Taco Bell contract for Southern California. After really growing his business to support the account, they called him up one day and told him that they were going to experiment with cleaning the windows themselves, and that they wouldn't be renewing their contract. This wasn't because of bad service--it was a bean counter-driven decision to save some $$. It was such a huge loss of business revenue (he had multiple employees and vehicles at the time) that he ended up having to file for bankruptcy protection, and ended up losing his home. Six months later, Taco Bell called him back and said that they had made a mistake, and they really wanted him to do their windows again. He took them back, but then immediately sold the contract to a competitor, and vowed to never again become so dependent on one source of business income. He's since recovered financially, but he's learned some important lessons along the way.