metrics and project success

I have come to a realization. Any project, no matter how small or big, should have a way to measure how sucessful it is. We should be able to define the metrics which would make a project sucessful and ways to measure those parameters. There should be a objective way to measure these metrics defined before we start the project. I am using the term project in a generic term - it may be something as mundane as learning chess (in which case the metric can be - I should be able to defeat the chess program at level 4) or something as challenging as losing weight.