Businesses have many aspects of their operation that are unpredictable: ask the legal team exactly what the result of a legal action will be, and when it will be completed by, and you'll get a fuzzy answer. Ask the marketing team exactly how many new signups will result from this new ad campaign and you'll get a fuzzy answer. Businesses can easily cope with unpredictability, this is not a problem.

The problem is that software development has not been treated as one of these unpredictable operations. It absolutely is unpredictable, we know this from decades of experience and all the academic research on the subject. But, probably because of history, politics and power imbalances, software dev teams have very rarely managed to convince executive teams that software development must be treated as unpredictable. As a result, software dev as a profession has a bad reputation for not delivering on their promises.

When we do manage to convince executive teams that software development is unpredictable, good things happen. The author's point that "tax software must be released at tax time" still happens, but the planning around the specific feature set takes into account that if the release date is fixed then the feature set in the release will not be. Again, it's not a problem to deal with the unpredictability, as long as everyone accepts that it is unpredictable.