FS, I disagree. If person cannot understand things from the first time, you explain again..and again.. Until either person understands the things, or you as a manager decide that this person doesn't fit the position. And yes, saying " you cannot get anything right" is direct abuse. If the person that your company hired for this position cannot get anything right, then your HR or whoever was hiring him/her should be replaced in the first place, as insuitable to his position. You can NOT abuse in any case, under any circumstances.