To quote Roseanne Roseannadana, "It just goes to show you. It's always something. If it's not one thing, it's another." When analyzing data, sometimes we feel very frustrated because just as one problem has been addressed, there is always another one just around the corner. It feels like it never ends, especially since we still need to meet each frustration and deal with it. When modeling, we need to pay attention to common problems, like those involving missing values, outliers, limits of detection, and unusual distributions, which can make all the difference between drawing the right conclusion – or the wrong one.