So, after my developers and I had discussed – at a rather detailed level – a new feature requested by one of our customers, I said: “So, I am going to need to know about how much effort it is going to take to get that done.”  

Steve McConnell: “The primary purpose of software estimation is not to predict a project’s outcome; it is to determine whether a project’s targets are realistic enough to allow the project to be controlled to meet them.”