How is it a "robust phenomenon" if it is negated by using strings of larger length difference in the head-tail example or by asking people to answer in the N out of 100 format? I am thinking that people have to learn reasoning to answer questions correctly, including questions about probability, for which the feedback they receive from the world is fairly noisy. And consequently they learn that fairly badly, or mislearn it all-together due to how more detailed accounts are more frequently the correct ones in their "training dataset" (which consists of detailed correct accounts of actual facts and fuzzy speculations). edit: Let's say, the notion that people are just generally not accounting for conjunction is sort of like Newtonian mechanics. In a hard science - physics - Newtonian mechanics was done for as a fundamental account of reality once conditions were found where it did not work. Didn't matter any how "robust" it was. In a soft science - psychology - an approximate notion persists in spite of this, as if it should be decided by some sort of game of tug between experiments in favour and against that notion. If we were doing physics like this, we would never have moved beyond Newtonian mechanics.