When presented with a tough spot, a protagonist manages to pull off awesomeness in getting out of it. Unfortunately for the character, however, they don't remember how they actually did it, and may not even remember what they did.
There are many reasons they won't recall what they did: it could be because they were "in the zone", acting on pure reflex because they didn't have time to think, that they have a Split Personality where one of the personalities can pull it off, but the other personality(ies) are unaware of things when that one personality is in control, they shut down anything not directly involved with surviving an encounter, or if supernatural powers are involved it may be a case of Die or Fly, and they're not aware of how they pulled off the awesomeness because the power isn't something they previously used.
Whatever the cause, they have no recollection of what they did, at times leaving them puzzled about the praise they're receiving or frustrated by their not knowing exactly what they did.
This can also be used for Take Our Word for It. If a writer wants to convey that their viewpoint character made a speech, argument, or comeback that's really, really awesome, it can be hard for a writer to convey that unless they are a really really awesome writer themselves. So one way around that is to show the character walking up to the podium or being the target of the insult, and then cut to the next scene where everyone reacts to their awesome speech/argument/comeback, without going into detail about what it actually is.
Similar to Laser-Guided Amnesia and Victory-Guided Amnesia, but whereas those amnesias are externally induced, Awesomeness Induced Amnesia is completely internal to the character and not caused by another party. Compare The Greatest Story Never Told, where the hero knows what they did but no one else does.
- In Old School, Will Ferrell's character Frank (who has never been shown to be anything more than average intelligence) is in a formal debate with a famous news pundit. After Frank delivers his argument, the pundit outright says that he has no response. When asked how Frank did that, he says he has no idea and that he blacked out.
- Heavily implied in Quantum of Solace, when 007 performs a Mook Horror Show with the Quantum thugs who try to stop him from escaping the Tosca show. The scene suddenly switches to black & white with jerky, erratic camera work, treating us to multiple disjointed shots of Bond violently fucking up bad guys with an utterly-blank facial expression. He seems to be running on autopilot, so to speak.
- In 1634: The Galileo Affair, Father Mazzare, the town priest for a 20th century coal mining town dumped into the middle of the Thirty Years' War, is tasked with speaking in defense of Galileo, at his trial for heresy. The speech isn't explicitly mentioned, but afterward he's congratulated for what he said. However, in a bit of a daze afterwards, he mentally mentions that he doesn't know what he actually did say in Galileo's defense.
- Unto the Breach: In a vengeful berserker rage about deaths from a trio of armed bunkers her overloaded helicopter is forced to fly over, Kacey takes the armed Hind helicopter back to the bunkers, and in a whirling dervish of destruction to the sounds of Dragonforce leaves them "fucking vaporized", as an observer to the carnage describes it. Afterward, however, in the narration it's noted that she doesn't remember any of it, between her vengeful thoughts and being "In The Zone".
- This happens all over the place in The Wheel of Time, where characters will do things they had never been able to before, either because they don't know they were supposed to be impossible, or because they're in such an emergency that they can only rely on instinct, and tap into some kind of spiritual Genetic Memory that allows them to discover new abilities. Rand in particular does this often, especially in the climactic battle the end of a given book.
- In The Death Gate Cycle, Alfred manages to pull off incredible feats of magic as he used to be a master wizard but adopted a bumbling, useless personality which took over to the point that he only shows his skills a few times and reverts to his bumbling personality with no memory of what he did.
- In Raising Steam, Moist von Lipwig kills several grags (Dwarven terrorists) in a blind rage after finding out that they'd killed some of the railway workers. Afterwards, he has no memory of doing it.
- Star Trek: The Next Generation: When Barcley gets a brain upgrade by some aliens, after it wears off he tells Troi that he remembers doing everything he did, he just doesn't remember how.
- Champions supplement Champions III. Mystery Powers was an optional rule that allowed the game master to spend some of a character's points on a power that neither the character nor the player knew about. The example given was of a character with a power that would activate whenever they were in great danger. It would hopefully deal with the threat, but would also cause the character to have no memory of what happened.
- In the Pathfinder roleplaying game, Caiden Cailean actually became a god by taking the Test of the Starstone, and doesn't remember how he succeeded. Though in his case, the amnesia is because he was dead drunk at the time.
- During the war between Aquaria and Airyglyph in Star Ocean: Till the End of Time, a Vendeeni ship appears out of the sky and begins to lay waste to the warring kingdoms. After seeing the wanton devastation and learning that the Vendeeni wish to capture him, Fayt unleashes his Destruction power to delete the ship from existence. The physical and mental trauma of the act leave him unable to remember how this happened. The fact that Cliff and Mirage were not surprised by this heavily implies that the same thing happened to Maria after she destroyed the Invisible.
- Casters in Erfworld can join into a "Caster Link", a type of Mental Fusion initiated by a Thinkamancer. If two casters participate in addition to the Thinkamancer then the resulting gestalt can create whole new spells or effects no single caster could even attempt. After such fusions, the individuals retain only vague memories of how they did it, but usually gain greater insight into their own discipline in general.
- In RWBY's Volume Three finale, Ruby witnesses Cinder murdering Pyrrha and a sudden burst of silver light erupts from her, washing out the screen. She wakes up some time later at home, with no idea what happened afterward. She is told that she turned a Grimm dragon to stone, and is unaware that she did something to Cinder that cost her an eye and at least her hand and rendered her unable to talk beyond a hoarse whisper.
- The Peanuts special "It's Your First Kiss, Charlie Brown" has our hero, Charlie Brown, giving the Little Red-Haired Girl the customary kiss...and after a state of euphoria, wakes up in bed the next morning with no memory of what happened after. Linus tells him later that he was the life of the homecoming dance, which Charlie Brown can't recall.
- In the Futurama episode "Time Keeps On Slippin'", the world experiences "time skips" - incidents in which time appears to skip forward because nobody remembers what happened in the intervening time. One of the last time skips is to Fry and Leela's wedding, which frustrates Fry because he can't imagine what he could possibly have done to get Leela to marry him. It turns out he rearranged the stars themselves to write his proposal.
- In Generator Rex, it is revealed that Rex has a last resort defense mechanism: a Humongous Mecha that has that one drawback of erasing his memories when used.