OoC: @Outis I should say that it works like so many other things. If the victim has their mind weakened they can't defend against such a thing, even if they normally could, being the equal or better of the other.
I've been doing some research on some events in Suikoden (been a while since I played any of them, been going mostly by memory). And in Suikoden 3 there seems to be an event that succeeds only because the villain made an effort to weaken his victim's mental defenses just beforehand. Otherwise, he wouldn't have been successful, at all. At least that seems to be what is implied and believed by fans.