Following the above link:

"7. Don’t reserve estimating for when you know least about the project – Estimation should not be reserved for the beginning of projects. Instead done throughout as we learn more about the emerging true requirements and ability of the team to build and evaluate software."

So the idea that you can calculate upfron how much time a task would take is a delusion and the best you can do about it is to make educated guesses which would become more and more accurate as completion of the task approaches?

If this is true then project management courses must start with some kind of initiation for changing the mindset of expectations, some "reality check", mustn't it?