Yup. For instance, he mentions interest rate. Why? How is it useful to think about it and precisely define it in this context?
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The "interest" is a metaphorical measure of how sustainable your situation is, and how urgently you need to address the "principal".
If you incur technical debt as a mismatch between your codebase and your requirements (owing to the evolution of requirements) initially you may just be able to work around the mismatch, but it starts to incur "extra" work - this has been called the "interest" in the extended metaphor. Everything you do that isn't addressing the mismatch keeps adding to the debt though, so eventually the "interest" becomes equal to your entire budget and no more forward progress can be made, and typically bankruptcy is called (give up on code base, propose rewrite to address the actual requirements) and the cycle starts again.
If you incur technical debt as a mismatch between your codebase and your requirements (owing to the evolution of requirements) initially you may just be able to work around the mismatch, but it starts to incur "extra" work - this has been called the "interest" in the extended metaphor. Everything you do that isn't addressing the mismatch keeps adding to the debt though, so eventually the "interest" becomes equal to your entire budget and no more forward progress can be made, and typically bankruptcy is called (give up on code base, propose rewrite to address the actual requirements) and the cycle starts again.