Running a simple on-line service with a small monthly subscription fee and a fair proportion of international customers, we literally lose more subscriptions because of unexplained card failures than all other causes put together
This one is easy, as I do something similar. Peoples cards expire, and they don't update their user data if they've been subscribed for a while.
In three months? No.
Mathematics deals exclusively with the relations of concepts to each other without consideration of their relation to experience. -- Albert Einstein