I have devoted my entire adult life to learning about money. That might sound like cruel-and-unusual punishment, but I’ve mostly enjoyed it. For more than three decades, I’ve spent my days perusing the business pages, reading finance books, scanning academic studies and talking to countless folks about their finances. Yet, despite this intense financial education, it took me a decade or more to learn many of life’s most important money lessons and, indeed, some key insights have only come to me in recent years. Here are 10 things I wish I’d been told in my 20s—or told more loudly, so...