It's a funny thing to agree so much with the content but not so much with the conclusion.
Well, that's not really an accurate description, it's more about what you want to do.
As a simple measure of success, surely, there's no substitute for reaching the goal. Once you've declared a goal, as long as you haven't reached it, no matter how many things you've set in motion, you haven't succeeded.
But accomplishing the goal isn't a good measure of progress. You set the goal as a matter of reaching there, while you are here. Between here and the goal, as you've also mentioned, there's that backtrack of obstacles that are between you and the goal.
If all you measure is whether you reached the goal, then at no point in time are you able to tell whether you're closer to the goal until you've reached it. There's nothing telling you if you're going the right way.
If my goal is to lower my weight from, say, 90kg to 70kg, if all I measure everyday is whether I am at 70kg, there will not only be no progress but also I will have no indication whether any action I may be taking is actually good.
I may read that I need to perhaps diet or exercise of sorts. But to tell whether it's working for me, I need metrics, like "what's my caloric intake vs caloric consumption?" - that's a metric that I can actually control, so that at the end of the day when I measure my progress (whether my weight is closer or not to target), I can take action on it (I may exercise more, eat less, or both).