It's a bad aphorism if you take it literally and don't think about any nuance, but it's the correct priority. In many cases each of the three steps can take longer than the last, and each step is useless if the previous step isn't possible. The lesson is supposed to be to focus on each step at a time, not to completely ignore the other steps.

If you're making a complicated webapp, use your favorite framework to make it functional, and then if it's functional and not already fast enough, look at the slowest parts and replace them with faster alternatives. It's not going to result in the most elegant solution, but in most cases it will be good enough. Better to have something that works than to spend an extra year reinventing the wheel.