The article is really cool even though it is a little bit simplistic in my view (and experience). I&#x27;ve also made this comment on the article by the way.
The first problem is that rarely steps are independent from each other. I haven&#x27;t seen hard data on this (and if they have hard data, they should look at it) but my guess is that if one step fell behind schedule, there&#x27;s an higher probability for the next step to fall behind schedule. That&#x27;s because the reason a step is behind schedule is not purely random but depends on the internal element of the project (it is harder than usual, using new tech, a person is overloaded and always late...) and all this problem will not magically disappear in the next steps.
The second issue is that project are not so simple as a sequence of task. They usually have tasks in parallel,with different dependencies and sync point. Accounting for time variations on each step quickly become a total mess.