There is a dangerous kind of boolean thinking here :
"Either you believe that luck is dominant, in which case, why bother with effort?
or
You believe that luck is random, in which case it can be eliminated from your thinking and you can focus on all the stuff you can control."
Life is full of stochastic processes which all have a bit of randomness to them. Luck actually does not exist. There is just random chance that some event may happen which a certain subjective point of view interprets as favorable.
Take poker as a simple example. There is random "luck" in that at each point in the game, certain sequences of cards could fall that are more or less favorable to the cards in your hand. You win money at poker by considering how likely each random outcome is and making rational decisions based on this.
I think the likelihood of each random or apparently random is just another factor in the decision making process. Just like in poker, it's a volume game - make good bets on likely outcomes and if you get screwed a few times it'll all even out if you play enough. Repetition is how we can get randomness under control.
There's no binary here between ignoring luck and fatalism, and most people inherently realize that even though luck is a factor the best they can do is improve their average result rather than completely controlling things. The best people in any field will focus on what they can control and not worry about the rest.
To me the problem is that people generally want to explain luck away in hindsight: the team that won the game on a last-second shot won because they "wanted it more," the business that comes out on top "executed better," etc. It even comes into play in ethics, whereby the exact same action (say, driving drunk) often has different outcomes (hitting someone versus making it home safely) that cause us to judge people completely differently.
In other words, people hate the thought of luck determining things, and thus we over-ascribe outcomes to individual differences, overly glorifying the winners and shaming/demonizing the losers.
When is it bad luck? Sometimes it's obvious you're making mistakes, not working on the right thing in the right way. Sometimes it's not. It would be nice to know.
Since when do you ever look back and say that you wouldn't do anything differently? That indicates you haven't learned anything, not that it was bad luck.
I usually go by "If I look back and can honestly say I wouldn't do anything differently given the information I had at the time, then it's bad luck." That doesn't mean that I made the right choices, or that I'd make the same choices in the future. But it means that I did the best I could with the information I had available to me, and didn't have any rational basis for choosing differently.
"I'm a great believer in luck, and I find the harder I work the more I have of it."