I'm constantly amazed at how many people don't understand the concepts of basic finance and how compound interest works.
Years ago, I brought my laptop with me to buy a car so I could plug all the numbers into a quick amortization schedule. The sales person offered me a choice of $1,500 cash back or 1.9% financing instead of the typical rate a few percentage points higher.
I plugged the numbers into my spreadsheet and saw taking the cash back would cost me a couple grand more than the lower finance rate. When I told him I wanted the finance rate instead of the cash back, he mentioned that I was the only person he'd seen not take the cash back.
Maybe he was pulling my chain, but in my experience, the average person doesn't know what compound interest is, let alone what an amortization schedule is.