Many systems either encourage you to post or share details which banks also use as security checks. And there are many games (What is your ‘pornstar’ name and the like) which between them gradually reveal details such as your first pet’s name, or the school you went to.
Xian decided to delete their Facebook profile after realising that all of their banking security question answers were either directly visible on it, or easily found by following links.
It was only somewhat later, when telling the tale of how hard they had found it to delete the information, that a student asked why they had given honest answers to the bank in the first place. As the student pointed out – it isn’t as though the bank checks the answers are true, you just have to remember what you told them.