While working on the predecessor site to The Professional Network, my brother with whom I was collaborating quoted some wise person saying that "perfect is the worst enemy of good enough." In other words, once something is good enough to do the job it's designed for, the worst thing you can do is to keep delaying its release till it's perfect. A related idea is that once it's good enough, you've probably got more important things to do than to keep tweaking the little imperfections. People who aren't satisfied with good enough sabatogue their own efforts by failing to benefit from the good enough work that they do.
The perfect website design probably doesn't exist. However, a good enough design is achievable.
As important as it is to be able to recognize when improvements on a design are not necessary, it's also important to know the difference between good enough and not good enough. PitWEoGE is not an excuse for jumping the gun and unveiling a design with flaws that will be dertimental to your goals.
It's also important to know when a particular feature of the site is good enough so that you don't keep working on what's ready, but never unveil the design because there are still parts that still need work.
Finally, "good enough" is not a phrase that stands alone--good enough for what? A website design that is good enough to be publicly unveiled may not be good enough, for example, to spend advertising dollars to bring people to. Also, a design that is good enough for the initial unveiling and even to begin promoting may not be good enough to leave as-is. In other words, once you've gotten everything done that's needed for initial launch, your next work priorities may be unrelated to the website, or they may be improvements to the website.
In summary, assess your priorities, work on the most important things first, and once one task is complete enough that additional work on it is not the top priority, shift gears and work on what has become the most important.