Hasn't everyone made a move, then cringe because you just dropped a piece and then you realize that the move was brilliant because it forces mate?
What is "luck" in chess?

Luck has been defined as "when preparation meets opportunity". So, I think luck in chess is 'mostly' about one player's preparation outperforming another's.
Of course, luck can also just be COMPLETELY random, like when you win the lottery. Chess is more a game of calculation, however there is PLENTY of "random" luck in chess, but in general... you simply bring up a great question! ha

Hasn't everyone made a move, then cringe because you just dropped a piece and then you realize that the move was brilliant because it forces mate?
That's called making a brilliant move, because it's brilliant.

When some s@#% distracts your opponent from seeing through your combination setup.

I am a lucky looser. I met a player rated 600 above me, and the big sensation was that he won. He punished openingmoves that I didnt really now was bad. Getting a good player to highlight my problems was luck. Now I work on those problems.
I just had this position, i was playing black. I moved my rook up to take the pawn and to threaten the other pawn. A few moves later, checkmate appeared when i wasn't even looking for that. That's got to be luck to some degree, hasn't it??

"Luck" in chess is the mysterious natural tendency for a better player to choose better lines over time than a weaker player. This is usually determined by the player's style as well. Tal was much "luckier" in crazy sacrificial lines than his contemporaries because they used passive defensive techniques and Tal's pieces were very, very active. Magnus has incredible "luck" even versus the world elite due to his energy sense. Some people call "luck" the same way they call "intuition", which is the idea I'm defining here.

I've often made mistakes that haven't been costly because the opponent (or computer) hasn't moved how i feared they would do. Most often, it's not a case of them not seeing it, it's a case of me having that move covered elsewhere. But if i didn't realise i'd already got that covered, that's luck right there!
OK, the better the player of the two is more likely to have moves covered all over the board anyway, but if you made a careless move without realising your back was covered, it's still pretty darn lucky in my book!
This is what's meant by luck in chess
Hasn't everyone sacrificed a piece for an attack that one is unsure of?