In An Iron Will, by Orison Swett Marden we read:

We hear a great deal of talk about genius, talent, luck, chance, cleverness, and fine manners playing a large part in one’s success. Leaving out luck and chance, all these elements are important factors. Yet the possession of any or all of them, unaccompanied by a definite aim, a determined purpose, will not insure success. Men drift into business. They drift into society. They drift into politics. They drift into what they fondly and but vainly imagine is religion. If winds and tides are favorable, all is well; if not, all is wrong. Stalker says: “Most men merely drift through life, and the work they do is determined by a hundred different circumstances; they might as well be doing anything else, or they would prefer to be doing nothing at all.” Yet whatever else may have been lacking in the giants of the race, the men who have been conspicuously successful have all had one characteristic in common–doggedness and persistence of purpose.

It does not matter how clever a youth may be, whether he leads his class in college or outshines all the other boys in his community, he will never succeed if he lacks this essential of determined persistence.

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Persistency of purpose is a power. It creates confidence in others. Everybody believes in the determined man. When he undertakes anything his battle is half won, because not only he himself, but every one who knows him, believes that he will accomplish whatever he sets out to do. People know that it is useless to oppose a man who uses his stumbling-blocks as stepping-stones; who is not afraid of defeat; who never, in spite of calumny or criticism, shrinks from his task; who never shirks responsibility; who always keeps his compass pointed to the north star of his purpose, no matter what storms may rage about him.

The persistent man never stops to consider whether he is succeeding or not. The only question with him is how to push ahead, to get a little farther along, a little nearer his goal. Whether it lead over mountains, rivers, or morasses, he must reach it. Every other consideration is sacrificed to this one dominant purpose.

The success of a dull or average youth and the failure of a brilliant one is a constant surprise in American history. But if the different cases are closely analyzed we shall find that the explanation lies in the staying power of the seemingly dull boy, the ability to stand firm as a rock under all circumstances, to allow nothing to divert him from his purpose.

I like the metaphor of the journey of a ship at sea. If the ship has no set course, no set destination, it could end up anywhere and will almost assuredly not end up anywhere useful. The ship will eventually get to port only if they continually check their course and move towards it. If there is a storm and the boat gets knocked off course, the crew can reset the course, point it back to the chosen destination, and press onward. If an island gets in the way, the ship just goes around it.

So it is with our goals. If we have unclear, constantly changing goals, we will end up wherever life takes us, probably not anywhere spectacular. If you we take note of where are life is going and act to accordingly, we reach our goals. When we have a setback, we can just pick ourselves up, dust ourselves off, and start again. If there is an obstacle in our way, we have to search until we find a way around it. If we set our goals and are relentless in pursuing them, we have no other option than to eventually attain them.