The majority of threads that I've seen people fail sn usually involve being found early and "saved". The few others are typically where they abort mission because the taste is too salty and yuck for them. The ones who manage to drink it and throw up(not due to taste, but nausea from the stomach rejecting it) seem to succeed, particularly when they have an extra glass or two as backup.
I really believe that it would succeed the majority of the time if people didn't get found or throw it up instantly. Don't take my word for it though. You can read through the various threads if you'd like to. Every failure I've seen in months as of now, is because they were found by a roommate or a family member.
Please don't quote me on this, but I remember seeing that an estimated 67% succeed, and that number would be in the ~90% range or so, if people did it correctly(meaning both executing the method correctly and not being found).
Best wishes in the meantime guys.