For some time the western world believed that if you could list every part of a thing, you understood that thing. Ludwig Von Bertanalfy changed that with general system theory. In GST things have interactions and you need to understand that. They have interfaces. Interactions may follow patterns, like strange attractors or cycles ammenable to Fourier analysis, or they may have cybernetic feedback.
Some such systems with many interactions may be complex. If you build a complex system you may need means to control and specify so many parts that no one person can grasp the whole thing. You may need system engineering. It has means to manage complexity.
Systems may be defined, like boxes. You may treat the internals as unknown and just specify the interfaces, black boxes. You may see inside and treat them as white boxes.
The enterprise is a system. Each IT investment is a system. Integrated sets of IT are systems. EA is meaningless without the concepts related to systems.
"If you do anything long enough, you eventually get good at it." MK