What he didn't yet know . . .

How effective do you find the sort of writing that goes along the lines of "What he didn't yet know . . ."?

By this I mean when the author is writing in proper narrative and is following the same time-line throughout, but suddenly cuts in with little snippets of the future-to-come that is, as of yet, unknown to the MC.

In 1st person POV I've seen it in terms of "That was the last time I saw my daughter alive" or "If only Jack had the good senses to reveal his secret to me then while I was still neck-deep in the investigation. It would be another month before I found out." (Sorry, I can't remember where these are from. I think the first one is Stephen King, but I'm having trouble remembering the author of the second one.)

These work fairly well in 1st person as it builds an excitement or anticipation for something to come. But have you found that it works equally well in 3rd Omni?

"He dismissed the obscure lithographs as the musings of a madman. Their intoxicating portrayals of life lived in agony would not be recognizable to him until after his final encounter with the Devil."

I realize it all depends on the story, but if in the above scenario we aren't even supposed to be aware that "he" is about to meet the Devil, would that feel like giving away too much prematurely?

What if it's used to indicate future events that go beyond the time-line of the story? In other words, unlike my King example where he sets the reader up by saying "That was the last time I saw my daughter alive" and then we stand on the edge of our seat waiting to find out what happens every time the daughter enters a scene (and eventually dies a few hundred pages later), it's something to the tune of a man who throws caution to the wind and eventually lands in prison. If the novel ends with his incarceration but the "what he didn't yet know" moment reflects on how he would later come to regret his choices if only he knew what having no freedom meant, that wouldn't be a shortcut because the story would never reach that moment. The MC within the story is acting foolishly because he has a juvenile understanding of imprisonment.

The above is just an example (not something I'm working on) but it brings to mind the true story of one of my uncles who wrote his story in his memoirs (I'll condense it as much as I can right now).

As a young man during the dictatorship in Greece he was hiding from the government in a small village. He was out hunting one day and accidentally shot another man in the chest (he didn't see the man when he fired his weapon). My uncle took him to the local doctor who saved his life, but that man turned out to be an undercover officer who was out looking for him. After he recovered he notified the authorities of my uncle's location and had him arrested. His memoirs actually focus only on the torture he endured while he was held captive.

Now my uncle always said that he should have let that man die in the woods (for obvious reasons). Not only did the man arrest my uncle but he was also the head guard in charge of torturing him.

Long after the dictatorship ended my uncle was working with a group that patrolled certain neighborhoods to help get drug addicts of the streets. He was approached by a man who offered him oral sex in exchange for money (according to my uncle the man looked like he'd been beaten by life to a miserable shell of a drug addicted man). My uncle recognized him as none other than that same guy he shot in the woods.

Now if I were to retell that story in 3rd person but have it end after my uncle was released from prison and I included that moment of "what he didn't yet know" it wouldn't be a shortcut because the story would never reach that point. It would be worth mentioning, but not workable as a viable ending to the tale.

I think that's closer to what I'm asking.