It can be. You can be lucky to meet the right co-founders. You can be lucky to have the right idea at the right time. You can be lucky in the sense that working on your current mediocre startup allowed you to luckily come upon a problem or idea that is even bigger. There is and always will be an element of luck to success. What it comes down to though is nurturing an environment where that luck is more likely to happen than not.

What if two people pick the same project independently of each other, work equally hard, and only one comes out successful. Did the one that did not come out ahead not work hard?

If your premise is that they both worked equally hard, why even ask such a pointless question?