[allenu]

I think that attitude is the right one. Make decisions as if you cannot predict the future and you will be on a better path than one where you think you can.

The way I look at it, you have the most unknowns and risk at the start of a project and the least at the end. As you work on it, you learn about the domain of your problem space and the possibilities and impossibilities of what you can do technically, as a result, those unknowns and risks go down. With that in mind, structure the work you do so as to front-load as much learning as possible to help reduce risk and get a better bearing on how long it will all take.

And yes, be able to cut features if that target date is more important than the ideal product goal you set out with.