The whole point of letting someone 'know' of the hex is related to the placebo effect.
I've seen 'hexes' work when the 'target' was/is unaware of the hex. Still...you must make the 'target' aware of the attack (like making the target receive the intended violence)
before you get results. A bullet does the same thing, the target may be totally unaware of the shooter and the gun but will still fall victim to the bullet as it hits them. There are
odd cases where the recipient is unconcious of being struck...onlt to find out years down the line of a bullet that is resident within their body! Odd, yes! Typical, NO!
Hexing can work in two ways...either through the placebo effect, where the victim convinces themselves of the eventuality of the hex working thereby having their own
subconcious alter their behavior so that they find themselves in harmful situations or that they actively believe the harm into being (psychosomatics) directly in their body.
The other way is by actually causing an attack upon the victim by whatever means the perpetrator wishes to use that is NOT actively known by the victim. There are ways
of alerting the recipients unconcious mind to an attack and then letting the placebo effect work or by actually causing harmful energies to enter the sphere of influence of the victim.
Sympathetic magic, contagion magic, etc. all encompass methods to bring about these influences. You also have defenses against these attacks...utilizing the exact same
methods of the attacker at your disposal in order to defend yourself! When dealing with the unseen it is handy to have astrong array of astral energy fields working. Psionics can
be countered. Magic can be countered. La Vey was dealing with the placebo effect when he was speaking on this. By using the placebo effect, the attacker doesn't have to
expend much personal energy to achieve his/her desired results. The human mind is extremely inventive when it comes to this! Demons have got nothing over the inventive
horror that human beings can inflict on themselves/others! Yuck!