If an employee ever gives the reason for employment termination as, “Pursuing Other Opportunities,” or something similar, you are in for some rough roads. We all know that the unspecified other opportunity is a very lucrative position with the competition, and they do not want you to know about it. You do not want them to leave, because you know that they will leak out all of your plans, and business dealings. This is really bad, because us an Overlord hopeful, your competition is another Overlord hopeful. Someone as ruthless as you. You do not want to make a counter offer, because you know they are unhappy under your employ, and may seek extra funds by selling company secrets on the side.
You are left with but a single option. Shoot to kill. You do not want your plans leaked. You do not want any possibility of it happening. Even if the individual had zero access and zero knowledge, you still want to prevent the other guy from having a top notch employee. You know they are top notch because otherwise, you would not have hired them.
A side benefit of this course of action is that employees will no longer be interested in pursuing other opportunities. If they know they will be shot, they are not going to be looking. If they are not looking, they will not know who to go to attempting to sale your secrets. You now have to work on ways of keeping them from going postal, but at least your secrets are safe.