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.
Exploited: The antagonist is well aware of and expects Alice and Bob's ability to eventually make really stupid mistakes.
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?"
Deconstructed: Suffering such a moment of unaccustomed stupidity causes Alice to lose self-confidence and damages her reputation among geologists.
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.