Loosely coupled systems are benefited from higher changeability. They are less rigid and more flexible because they are loose but still connected as they are coupled. On the other hand, they could behave unpredictably in the course of sudden change. While many studies and industrial practices are trying to make PLC-based control and automation software more loosely coupled, this paper aims to bring the attention of subject matter experts to the fact that making PLCbased control and automation software too loosely coupled could demolish the main characteristic of these systems, which relies on their predictability and reliability.