Which misses the point. Of course you have to be good AND lucky to succeed. But not everyone can be lucky. So think of that the next time you're looking a few rungs down the ladder.
However, I'm not advocating a cynical mindset. I'm advocating a compassionate one, and a realistic one. If you don't think luck matters, you can delude yourself into thinking the people below you didn't work hard enough, or that you must be especially talented and driven to have gotten where you are.
I've also seen people hurt themselves with that mindset. The guy who risks everything on some business venture that's doomed to fail, yet he thinks he can beat the odds because he's smarter or more hard-working.
How about having an absurdist approach towards luck. "I'm probably going to fail, and I'm going to do it anyway." It's honest, it's compassionate, and it doesn't discourage you from trying the impossible. That's how I think, and it's worked well for me.
Attributing things too much to luck in your own endeavours might lead to learned helplessness, among other things. Whereas assuming that the bum on the streets quite possibly got into his predicament because of bad luck seems like a safer and more compassionate assumption to make.
But factually speaking, I'd say much more than we'd like to admit is out of our control, which is one of the reasons why I am in favor of societies with strong safety nets and hefty base-line of compassion.
The population distribution need not be normal.