The financial decisions we make on a daily basis, even some relatively small ones, can have a huge impact on our future. That's because of the power of compounding. We understand that a relatively small sum saved over time can grow into a very large amount in the future. But we rarely recognize how compounding can work for or against us in our purchasing decisions, which are more frequent and significant than savings decisions. This is an area where the concept of opportunity cost can be especially helpful.