For some people, this question is really easy, but for my brain that is far too literal for my own good, it is really hard. I can't even write a good definition of it for the sake of this post. Luck is so hard to define, yet I say it all the time. The dictonary says it is "a force that brings good fortune", but is it really? The other definition listed there is "favoring chance", which I think aligns better with the common usage. The thing is, statistics and numbers are weird. If you were to spin a slot machine that has a 90% of giving you a jackpot and get a jackpot, is that luck? Statistically, it is very likely to get that outcome, but our speech seems to not reflect this. Most people will say that you're lucky if you get a jackpot on that, but it would actually be statistically less likely to get the 10% where you lose and get nothing, yet it is still called unlucky. Maybe, statistics don't exactly play into what we call "luck", but the favorable outcome does?