Fear is a primary motivator of ISTJs. The majority of our actions can be traced either directly or indirectly, to fear. We have individual fears, and we have fears common to our type. They all play a role.
No ISTJ will set out to control someone. We find that a repugnant behavior. We set out to control a task, and the people near us, particularly those either directly connected to us as a person, or connected to the task, end up being controlled--without our own realization.
And we qualify it, if we are confronted with it. Remember, we didn't set out to control others--it's a natural extension of our focus on the task--people are a resource and we tend to manage them as such. So we can easily and logically rationalize our controlling behaviors.