Wall of Force

No spell effect can pass through a wall of force even though you can see through the wall. This is because the space on the opposite side of a wall of force from you is under total cover. Just as you can't cast a mind sliver around a wall, you can not cast a mind sliver through a wall of force. Note that you can teleport (such as with a misty step, but NOT with a soul knife's thrown weapon teleportation) out of a wall of force to a place that you can see including through the wall as teleportation magic does not cause a spell effect to travel through the wall.