A while back I heard a great saying that's stuck with me: "Testing is the process". The phrase resonated for a couple of reasons.

First, it's the most succinct way to describe the process of testing and iterating. The process has been well documented... for example, Optimizely phrased it "Experiment, launch, iterate, repeat". Other good reads of this are out there, like "Create. Test. Learn. Repeat.". The concept is that product development is a process that is never complete. Try something, test it, revise it, rinse and repeat. Even when you've reached the pinnacle for the product, external circumstances like the market, competition, or technology can (and will) shift, requiring a shift in your product.

Second (the reason that resonated with me the most), is that the phrase creates leniency for yourself and those around you. This applies to not only product development, but almost every other aspect in life. Perfection is not expected and it's not the goal. Instead, if you go into each project with the mindset that testing is the process, you give yourself permission to fail, because testing implies failure is part of the process.

Sure, eventually you want to get it "right", so shoot for that, but recognize that the goalpost will move. Then do it all over again. Testing is not a part of the process, testing IS the process.