What do you wish you knew about money 10 years ago

Finally back from all that traveling: one week, four cities, three states. Yeesh.

The last leg of my trip inspired this post. I spoke to students at my alma mater, Coppin State University, about 10 things they need to know in life and about budgeting and money. What was interesting was that of all the questions I got on that trip, the thing students were most curious about was when I told them I don't like getting a big tax return at the end of the year. They didn't understand (like I didn't at that age), that getting a tax return only meant the government was giving them back money that they shouldn't have paid in the first place.

That got me thinking: what are some other things that you wish you'd known about money, say, 10 years ago, that you didn't know now? Leave your answers in the comments.