The way I've come to see it is "The less you know about a subject, the less you think you don't know."
In other words, you have no solid grasp on the field and so cannot make an effective guess at your ability in the field - so go for middle of the road and that's possibly your best statistical guess...
In other words, you have no solid grasp on the field and so cannot make an effective guess at your ability in the field - so go for middle of the road and that's possibly your best statistical guess...