I agree with the quote "perfect is the enemy of good", and I'll be the first to compromise.

Here is the problem: Ask 100 people to define their idea of a "Perfect" something (user interface, president, pizza, anything) and you'll get 100 different answers. Perfect is a subjective concept that is artificially made objective only within the context of a set of documented requirements, which ideally the group has collectively and intelligently settled on.

However, we typically don't start out with anything close to Perfect information, and external circumstances or new information make the stated goals of the requirements no longer optimal, functional, or useful. At that point the team would ideally change the requirements and thus change the definition of Perfect. If not, then Perfect is the enemy of good.