The paper uses the term "technical debt" without defining it. From the context the term is used in its popular sense in which the primary source of debt is writing code poorly. Ward Cunningham, who coined the term, did not mean it in this way [1]. Wikipedia defines it as "the implied cost of additional rework caused by choosing an easy (limited) solution now instead of using a better approach that would take longer" [2] which is more aligned with Ward's intention. The problem with the current understanding of the technical debt metaphor is that it justifies poor code quality. Apparently it's like taking out a loan to make a sound investment.