Extinction in a branching process: fittest strategies cannot guarantee survival

I very much prefer the classic structure of a scientific article. In my experience, articles that do not adhere to the classic structure have other errors in their content.

This article has only examples in the "results" section but no results. Additionally, the section is the same as the discussion section. The conclusions do not only conclude but show further discussion.

Finally, I would have liked to see a verbal explanation or interpretation on why "strategies with high fitness can also have high probabilities of extinction".