@7 fortune plays a huge role, but luck is opportunity plus preparation.
one of the themes that stuck with me from the Godfather (Puzo's book, not the movie) was the continual references to "playing the percentage points" - small incremental decisions and wise acts of foresight, none of which alone would ensure success but compounded to the benefit of whoever had better insight
this example not the basis of my saying that but it's the only way I can describe it; this is why there is such an emphasis on military tradition - success in war, for all it's sordid filth, is the result of cultural ethos difficult to fake.