Sure, luck is often involved in meteoric success. That's not to say that one must be lucky to be sufficiently successful. Set your sights a little lower than Bill's fortune.
Also, it's worth noticing that wild success is probably possible without luck, but is certainly impossible without hard work and discipline. Focus on what you can control.
One must be at least slightly lucky in order to not undergo a total existence failure due to random quantum fluctuations.
One can't change their luck.
So at the start of an undertaking, it can only be self-defeating to acknowledge it.
Though at the failure of an undertaking, it's certainly cathartic to curse it.
"One can't change their luck."
You can only give yourself more chances to get lucky.
And yet for some reason we treat pre-existing advantages differently than advantage of opportunity. Why?
Entrepreneurs with good fortune shrug their shoulders and accept it while those who inherit money so often feel guilty and are embarrassed by their good fortune.
If you think from the perspective of the actual doer, it might be an admissible, perhaps even superior strategy to focus on "hard work" and "discipline" (where is the difference, btw?) and leave out "luck". But actually, when you're honest about it and take the perspective of an observer, you'd be foolish to focus on those things because you'd see that for every great success that worked hard to get there, there are at least a hundred "failures" (let's just take the conventional notions here) who worked equally hard. It's kind of demotivating though to have to realize that all your hard work is merely the necessary condition of success and that in the end it will be luck that will make the real difference.
Bill Gates didn't become rich just because he worked his ass off. He also had crucial connections (including his parents) that landed him contracts with IBM and others.