Everyone in this business knows what a borrower's monthly payment looks like. Principal, interest, taxes, insurance, the classic PITI stack. What's getting more attention lately, and rightly so, is everything that doesn't fit neatly into that acronym. It's not a new problem. But in a market where affordability is already strained and debt-to-income ratios are doing a lot of heavy lifting at the qualification stage, the gap between "qualifying" and "sustaining" is worth talking about more...