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Sounds like a lampshaded Deus ex Machina. In the second case a lampshaded The Password Is Always "Swordfish".
I suppose there could be some cross-over with Deus ex Machina, but that's specifically an ending trope that resolves the overall plot or conflict. This, on the other hand, is just the protagonist being skeptical about an easy way to deal with a seemingly difficult or even insurmountable obstacle. That's not really the same thing.
As for the second case, I agree that also qualifies as an example of The Password Is Always "Swordfish", but, again, it's not really the same thing. The reaction to the character learning that the password is, indeed, Swordfish is what I'm referring to here.

Does this trope have a page yet? I've tried a few searches and can't find it.
Alice and Bob need to accomplish something very important but seemingly very difficult. While scouting the situation, they notice what appears to be a very easy way to achieve their goal. One or both of them say, "It can't be that easy!" Then they try that method and learn that, yes, it really is that easy.
Examples:
Spider-Man: Into the Spider-Verse: When trying to sneak into the Kingpin's headquarters during a black tie dinner event, the spider-crew notice the waiters are all wearing SpiderMan costumes. SpiderMan-Noir says, "It can't be that easy!" Smash cut to a few minutes later as they're all just walking right in and blending in perfectly.
WarGames: Main character David is trying to log into the WOPR computer system to undo the damage he's done, using Dr. Falken's backdoor access, but he doesn't know the password. He learns that Dr. Falken lost his son, Joshua, years ago, and says, "It can't be that easy." He still tries typing Joshua as the password, and it works.
Possibly a sub-trope of "Eureka!" Moment? But even if it is, I still can't find it.
Edited by Mr_Math