One of the most important lessons of key account management: having a single account take up more than 20 percent of your profit and loss statement (P/L) is business suicide. Unfortunately, many executives don’t follow this sage advice – which results in broken businesses, laid-off employees, and the loss of entrepreneurial dreams. We get it, it’s hard to turn down a big pot of gold from a big name account. That said, executives are paid to make the tough decisions.…