You know the game. You start with a deck of playing cards and slowly begin to stack them together, carefully leaning one card against another at just the right angle, until you've created a solid wall of cards. You build the house higher and higher, one card and one row at a time, all the while moving around carefully so the whole thing doesn't come crashing down. Building and growing a business can sometimes feel like building a house of cards. If you have one or two clients providing the bulk of your revenue, your business can begin to feel as precariously unstable as that playing card wall. Wal-mart is a giant corporation. Stories abound of how they've made and also broken some of their vendors. But you don't have to be a Wal-mart vendor to find your company in this tricky situation. No matter how safe you think your relationship with a large account might be, life tends to throw you curveballs. There are no guarantees. If that one large account leaves fo...