Unlike monetary debt, technical debt is difficult to quantify.
Technical debt is often the result of a poor understanding of the problem domain.
There is little point refactoring code without first improving our understanding of the problem.
Clean code is no use without a solid understanding of the business domain.
There is no absolute truth, just better models.
It can be difficult to turn reality into data.
Models are contextual. When the business domain changes, we must adapt our model. Shoehorning support for a new category into an existing entity will come back to bite in the future when things change again.
