Idiot Ball/Playing With

Basic Trope: Characters are stupid whenever the plot requires it, even when this contradicts established characterization.

Straight: Alice and Bob are seasoned cave explorers in an unfamiliar location with limited food and supplies. When faced with a Y-intersection, Alice suggests they split up.
Exaggerated: Alice is an award-winning cave explorer with several PhDs in geology, but when she sees a load-bearing stone column, she breaks it with a hammer just to see what will happen.
Justified: Alice is in a mentally-altered state due to exhaustion, oxygen-deprivation, or strange chemicals in the cave.
Inverted: Smart Ball
Subverted: Alice was kidding.
Double Subverted: She wanted to play Hide-and-Seek instead.
Parodied: A literal Idiot Ball falls from the ceiling and lands in Alice's hands just at that moment.
Deconstructed: Suffering such a moment of unaccustomed stupidity causes Alice to lose self-confidence and damages her reputation among geologists.
Reconstructed: Her action, while hardly wise, wound up putting Alice and Bob in just the right place to make an important discovery, leading them to conclude it was a felix culpa.
- Alice's moment of incredible stupidity throws the villain off, causing them to fall into a state of paranoia as they can't believe that Alice would make such a stupid mistake.
Zig Zagged: Alice, the world famous geologists ends up trying to hug Emperor Evulz to resolve it peacefully. Then it turns out it was a ruse to stick C4 to him. However, the whole reason Evulz's was a threat was that his armor was immune to normal weapons. Just as he was about to stab Alice, Bob shoots him with the magical bullets he prepared while Alice was distracting him.
Averted: Alice's actions reflect her intellect and experience as established up to this point, and her errors are all understandable and in character.
Enforced: "I know they have to be master explorers to navigate that far into the Caves of Doom, but we need an excuse for them to go into the deeper tunnels, so let's hand Alice the Idiot Ball."
Lampshaded: "Split up? Alice, let's not pick right now to do something incredibly stupid."
Invoked: Alice and Bob go through several intersections without making the Idiot Ball decision of splitting up. Then they come across yet another Y-intersection, they suddenly decide to split up for no reason, or, worse yet, the two of them just absent-mindedly walk into the two different tunnels, splitting up without even noticing it.
Defied: The author takes pains to make sure that everyone takes the best decision at the time given what the character knew and would be reasonably expected to know.
Discussed: As they reach the intersection Alice says, "Stay close to me, okay? And for the love of God, don't say 'Hey, let's split up so we can cover more area!' This isn't a movie."
Conversed: Alice says, by way of Seinfeldian Conversation: "I knew these two guys once, Charlie and Dean. Award-winning cave explorers, both of them. One time they went into a maze of tunnels, kinda like this one. They come across a Y-intersection, and for some reason - I'm thinking temporary insanity - they decide to split up. Both get lost. Charlie wanders around the labyrinth for about a week, manages to find a way out by sheer luck. Dean wasn't so lucky; he never got out, and the search party never even found his body. Pretty stupid way to go, huh?"

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