Technical debt is a very artificial concept. With real financial debt one knows immediately the exact dollar amount, the interest rate, the payment terms and so forth. There is usually no ambiguity or judgment. In contrast, technical debt is based on theories about software development and uncertain predictions about future changes to the software. As the old saying goes: "prediction is hard, especially about the future."

As a business, if I buy a computer on a company credit card, I know immediately that I owe $1200.00 at 23 percent interest per year. In contrast, if I develop a piece of software and decide to use global variables to speed up development, I may immediately gain a mythical man-month in development time BUT I have no idea how much it may slow me down in the future if at all. Sometimes global variables are the way to go and development will be consistently faster for the entire lifetime of the software compared to using local variables. This tends to happen, not surprisingly, when the data in the global variables needs to be used widely throughout the program.