I agree with all of the above, but in response to the original question I'd say there is a difference between how it plays out in striking vs grappling.
In striking, a fighter who has a knockout punch can potentially defeat a much superior opponent whose concentration lapses for a split second.
In grappling, it takes longer than a split second of lapsed concentration to end a fight, unless the fighters are already in an even position. If you are going against a much better grappler, you are unlikely to ever be in that even position. Even if you do get the opportunity to slap on a submission or start a throw, the superior grappler has some time to get their head back in the game and react and potentially counter the attack.
The only time I'd consider someone getting "lucky" against me during wrestling...
I made a mistake against an opponent who wasn't very good and ended up on my back. That wasn't the lucky part.
The lucky part was the buzzer went off, so I stopped wrestling. The referee called me pinned at least a full second after the buzzer went off. The entire crowd booed, even the visiting fans. My coach was a mellow guy when he needed to be, and calmly (although you could see his rage in his eyes) asked the referee "was he pinned right before the buzzer, you slapped the mat afterwards?" in an attempt to give the guy the benefit of the doubt. The referee responded "I didn't hear any buzzer. I have no idea what everyone's complaining about." I'd call that one luck. Lucky for him.
You'd think I'd get some sympathy from my coach. Nope. He said "There's a way to avoid getting a bulls$&t call against you like that - STAY OFF YOUR FU$&ING BACK!!! THERE'S ABSOLUTELY NO EXCUSE FOR YOU TO HAVE BEEN ON YOUR BACK IN THE FIRST PLACE!!!"
Being the last guy on my team to lose, that cost us the dual meet. The two heavier guys after me both pinned their opponents, but it wasn't enough. It still stings, and I still remember it quite vividly 25 years later (it was about February 1992).
The whole gym heard it, word for word. And he was absolutely right. I had nothing at all to say, so I nodded my head and sat down. I never stopped again until I heard any referee clearly tell me to.
The only instance of luck I can think of for or against me personally. But again, I shouldn't have been on my back in the first place, so I let him get lucky.
Edit: I wrestled the same guy again a few weeks later in a tournament. I pinned him in 24 seconds. No way I was giving him any chance at anything. What did my eloquent coach say after that? "That's what you should've done a couple weeks ago. I'm glad you learned your lesson." He pretty much only spoke the truth
