If you use your sun visors a lot, this is just going to happen - there are no 2 ways around it.

Mine? I was moving the car from one side of the driveway to the other, I flipped the sun visor down so I could remove the window shade out of the way and the plastic just cracked and came apart. Super lame.

Anyway, I see a lot of these popping up on the forums, so it looks like it's a pretty common thing for all the related Subaru/Toyota/Scion cars. It doesn't require them to be mis-treated or anything, they just sort of give up randomly.

The crappy thing is you cannot just buy the little plastic piece - you'll need to buy a whole new visor.