[HarrietTubgirl]

Here's the main thing that fucks this all up: there are a very limited set of brainteasers out there.

This means that if someone gets your brainteaser right in an interview, there's, say, a 90% chance that they've heard a question just like it before (or one with a similar "trick"). The false positive rate is too high. Many people know the answers to brainteasers far beyond their ability.

If you were to ask a completely new brainteaser, as difficult as the canonical ones, but requiring a different trick, you would get a very low success rate.

Side note: there's too much criticism on HN about "what does this question have to do with my day-to-day job". This is a bullshit point. The point of a brainteaser is to test problem solving ability, creativity, etc. It may not do a very good job of that, but just because you won't be "reversing sentences in place" in your job doesn't mean that the question is invalid. Think about what the question is trying to test.