It is possible to fail on the personality questionnaire.
I did stage 1 in February, then the the personality questionnaire 12 (working days) later, then after submitting the questionnaire, I got an email about 6-7 days later saying I had been unsuccessful.
I'm not sure if if the personality questionnaire is the sole reason for people not progressing. In my own case, I am confident I did well in the psycometric aptitude tests, but I let myself down in the motivation paper - and so I think the personality questionnaire was the final nail in the coffin on top of a not great motivation paper.
I didn't come accross this forum until after stage one! and since then I have read every single page, and I intend to keep reading it until I reapply next year.
I now have a year to learn that prep material! Fingers crossed.
i just wish i didn't have to wait a whole year - I am making a career change and I want this to be it. The year long wait to reapply is so much worse than the 15 day wait to hear if I'd passed the initial tests!
Good luck to everyone.