I think the article is a convoluted way of saying "use your judgement". The cost of adopting certain design, per the article, is not a real number, it is an est

I think the article is a convoluted way of saying "use your judgement". The cost of adopting certain design, per the article, is not a real number, it is an estimate. The probability of needing a feature, P2, per the article, is also not a real number but an estimate. What's so hard to estimate in software world is because the shear amounts of unknown. An abstraction leaking library, a not-fitting-exactly-your-use-case SaaS, ever changing standards, end-of-life of mission critical component, no-easy-fix vulnerability, emotional stress from team member, a dying cat, a never stop talking non-engineering colleague, there are more than "code" in software. Be prepared for change