The first time I have started to “see” systems everywhere was after reading the book “The Leaders Handbook” by Peter Scholtes. Seeing systems is like having night vision goggles, you turn them on and you start to see things, that you would not be able normally with your senses. I did know about embedded systems, but I did not know that it is possible to view everything as a system.
So, what is a system:
– is a regularly interacting or interdependent group of items forming a unified whole. Every system is delineated by its spatial and temporal boundaries, surrounded and influenced by its environment, described by its structure and purpose and expressed in its functioning.

This definition might sound like system is used to describe (mechanical) machines, and in the age of the machines, it was, since the term itself originates from thermodynamics. ( there was even a theory
later about the human brain being a machine.) And somehow humans tend to be limited to have only  mechanical theories..

But this definition above will not help you see systems, because there can be millions of items, multiple purposes. The trick is to consider the significant parts, the main purpose,  and organize all of them into separate views.
Now we just switch to Systems Modeling In simple terms you create a system type model of  everything you want and study it. Because it is a model ( everything is a model! even what you call reality is a mental model based on your senses ) the conclusions/results will depend on the accuracy of the model…
As a simple example example let’s take the human body.
– Digestive system ( Purpose: transform energy for the body ; Parts: you know them.. )
– Nervous system (  Purpose: transmit signals ; Parts: you know them )
– etc . ( the entire list is here )

So we might say that the body is a system of systems.. What is its purpose ?   (The whole should be  greater than the sum of its parts.. 😉
Go to the mirror and try to see yourself as a system. What can you say about the state of your subsystems ?  What is your purpose ? And what is your fuel?
Do it!

If you consider the greater you, then you can look at your life as a system. And even the whole world.

But there is a better model : the network !

If you want you can still reduce a network model to a system model, but you have to be careful not to eliminate some significant relationships, or items.
If  we go back to the small exercise above: How would you model your body as a network ? ( maybe you need a database ? )
An interesting experience that I had was acupuncture. I was able to feel how it worked, but wanted to know how it worked. After some extensive searching I was able to understand enough…
As I understood the traditional chinese medicine created a model of the human body ( with the qi, meridians,  points, and the balance between them ). I think  the chinese masters created/used a network model of the human body, even before network thinking existed…

A few years ago I saw an article about sequel to “The Leader’s Handbook”. I was interested because it was recommended by Ed Yourdon :
– Management 3.0 
I think it is an iteration over “The Leader’s Handbook” ( Management 1.0 ) because it introduces the “views“. Still it does not have the network thinking in it…
These books tend to reduce the complex human world to systems…
Because systems can be managed!  Did not find much on managing a human enterprise network…
Actually as Simon Sinek puts it:
“Manage systems, not people. Nobody wants to be managed.. People have to be led”.