Ys, you are right, fear of failure motivates us to try and get things done without failing. It makes us prepare more, try to learn more, practice more, etc.
The problem is that there must be a balance between that, and your capacity to act, independently of your fear. I would say that when people exclaim "don't fear failure" what they're actually saying is "try often, keep trying and don't let failure obfuscate your desire to learn and try again".
As in every thing, it's neither as simple as "don't fear failure" or "strive for perfection". A balance must be struck, because you'll never get it right on the first try, and so must try as many times as it takes to get it right. But without the proper preparation, without the proper thinking, adapting, understanding, reading, your ability to get it right at all will be greatly reduced.