Every March, people obsess over the top seeds. They study the matchups. They spend hours convinced this bracket will hold. Then a team nobody was watching takes down the favorite. In retirement, there is a version of that same upset. It does not happen in the stock market. It happens on your tax return. And unlike a busted bracket, it costs a lot more than bragging rights. The threat no one is talking about Most retirement conversations focus on portfolio performance. How did the market do?...