That's only if you're purely random. The point was preventing easily researched information undermining your account. To point, one of the questions for a service is : name of your favourite restaurant. If people were to 'know' me, they'd guess ones I went to, and might even guess/know the right one. The problem for them is the answer I chose IS the name of the restaurant, just in a different language. There is next to no memory effort required for me, but it isn't something you'd find from facebook or twitter or asking a best friend. Basically it's using 'jedi truth' for your answers and understanding of the question.
Might not work for some, works easily for me, and is entirely limited to the asinine security questions we get demanded to use. I'm not arguing the merit or lack of security questions, only that they need not be a huge flaw some portray them as.