NEW YORK ( TheStreet) -- Let's face it, personal finance isn't nuclear physics.The basics are so simple that anyone can get the concepts down in less than a day -- spend less than you earn, save and invest the rest. Knowing what should be done and actually doing it, however, are two different things. Most people realize that spending more money than they have is a bad, bad thing. That still doesn't keep millions of people from racking up credit-card debt. Here are 10 money lessons I wish I had known when I was 20 (I'm now 42 years old), which also have the power to change your life if you are able to embrace them.