Most customers have multiple accounts. I want to test as many scenarios as possible. I could write a test to select customers with 1 account, another to test customers with 2 accounts, another test with 3 and so on. Where do I stop? How many tests will I need? We have a customer with 130 accounts! All my tests work with random selections of customers so that as I run them over and again, I'm testing different customers. If I fix the number of accounts, then I'll certainly excluding the customers that don't have that number of accounts!