I'm reminded of a couple of stories where a character is pinned and unable to attack their opponent... unless they stab themselves, driving their sword through their own body to stab their opponent in turn.

That's a large part of the reason why berserkers are so terrrifying irl. There's no magical immunity to harm conferred by the berserk state. But if someone genuinely does not care if they die as long as they kill you it opens up many options that are difficult or impossible to defend against. Suicide bombers would be a more widely understood example; The hardest part of setting a bomb is often escaping. If you take that out of the equation it becomes much easier to blow things up.

related to the berserker thing, there's a concept in sword fighting sometimes referred to as 'newbie-fu', along with a lot of other names. Sometimes new fighters will do something so suicidaly stupid that experienced swordsmen have no defense against it. Not because there is no way to defend against it, but because whatever the newbie is doing is so dumb, and usually so suicidal, that no experienced fighter would ever try it. And because no one would try it, no one practices defenses and counters to it. Every so often a newbie will try something they saw in an anime and it'll work simply because no one ever bothered to craft a defense against such an outlandish attack.

A real world example i can think of is a series of French prison breakouts where the attackers evaluated all the defenses preventing them from getting in to the interior of the prison - Walls, fences, doors, cells, etc., and decided that the easiest way to breach all of them was to land a helicopter in the prison courtyard, get their guy on board, and fly away. None of the prison defenses mattered because the designers had simply not considered such a vector of attack.

I think some related TvTropes tropes would be things like "refuge in audacity". Or the idea that if you're wearing the right clothes and look confident you can go almost anywhere.