Testing one user early in the project is better than testing 50 near the end. If you make it into a big deal, you won’t do it early enough or often enough to get the most out of it. A simple test early - while you still have time to use what you learn from it - is always more valuable than a sophisticated test later.
Don’t make me think
Being an expert in online usability Krug gathered his experience in a wonderful book. This summary of key thoughts will help you to remember most important principles and laws.