People lie, Clary.

[ He doesn’t mean that to sound harsh, though in his matter of fact tone, it probably does. ]

Often, without remorse, and particularly when they think they can get away with it. That resource is open to everyone. To use it may, to an extent, give you an advantage. To avoid it puts you at a distinct disadvantage. A needless one. These people are not all your friends. You must know that by now.