If I want to curse my enemy I say the curse to him. As a result, he will become sick and have a lot of bad luck.
However, if he puts his fingers in his ears or uses some kind of earplug, I have to shout to make him hear it.
Personal experience tells me that even the best of earplugs are not perfect sound insulators. We are in a medieval type setting so no electronic noise cancelling is possible.
So, let us assume I meet my enemy and shout my curse at the top of my lungs. There is now a problem. The curse will affect anyone who hears (and understands) it.
How can I focus my shouted curse on my enemy without cursing other people in the vicinity. (It is impossible to curse myself)