I suspect that the failures had more to do with the people not being vulnerable to this particular memory than them not being vulnerable to memory implantation. For example, if your parents had trouble putting food on the table day to day the idea that they managed to buy a hot air balloon ride for you is obviously absurd.
How did they know the subjects had never been in a hot air balloon before? I’d apparently been up in one as a child, but didn’t remember it until I went up in one as an adult (verified with parents fwiw). So it’s certainly possible some percentage of subjects may just needed a trigger and had actually been up in a balloon before.
But that wouldn’t explain that exact implanted memory. If you went up as a 5 year old, that shouldn’t impact a false memory drawn from a picture of when you were 20.
May well be the case. The susceptibility to hypnotic suggestions depends on the receiver and the giver of the suggestions, and who the relation between the two is. Maybe in some cases there was, for some reason, more trust in the person showing the fotos, and in other cases less.
