I like the way Ben Horowitz puts it in his good pm, bad pm document:

Good product managers focus the team on revenue and customers. Bad product managers focus team on how many features Microsoft is building. Good product managers define good products that can be executed with a strong effort. Bad product managers define good products that can’t be executed or let engineering build whatever they want (i.e. solve the hardest problem).

As an engineer, I want to find the demons that are out there in the problem space and assault them, I want to eliminate all weakness from my precious software. But from the business POV I know we need to provide value to customers quickly and efficiently with the available resources, which is usually not the same thing.