said by CylonRed:
Problem is remembering what was used - that is why people answer them 'honestly' and truthfully. Many have to use the questions to begin with that by the time it is needed - people do not remember the one they used.
I totally agree that it's easy to forget, and that's why consistency is key to remembering what these alternative answers are. That way when you do have to use the reminder it's not that hard to remember the alternative set - Far less hard than remembering passwords which always should be unique and not consistent.
Even more secure is mixing them up, as Snowy suggests too, but still using consistent alternate answers is still a far better system to have something else, anything else, than data that can be found elsewhere such as public records or even through social engineering.