The problem is that anything which you remember that well is likely to be discoverable by other people. For instance, if someone's mother is dead there's a good chance that her obituary will be online and list the names of her children and her maiden name. Likewise, you could find the name of a person's elementary school via looking at their posts on Facebook in many cases - or if not their posts, then their siblings or their friends. So these kinds of questions are hardly a great proof of identity if it can be found online with a bit of searching.