Using the outside view tells you something about your particular case. If you don't know how long your project is going to take, and then someone tells you that such projects normally take ten months, then you've learned something about how long your project will take. It will take about ten months. Your quote is the kind of thing that people say because they think their project is special in some way. They're trying to fight the outside view. But most of the time their project isn't special, it will take just as long as everyone else.

The outside view informs judgements of particular cases.