This may be the longest explanation you will ever encounter on filling a glass with water, yet this example serves to point out a very important characteristic.
The assumption is that I begin with a an empty water glass, the current water level, and a desire for the glass to be full, the desired water level. The desired water level interacts with the current water level to produce a gap between what I have and what I want. This gap then adds to my motivation . My motivation then adds to the extent the faucet is open, because I turn it. The extent the faucet is open adds to the water flow rate. The water flow rate then adds to the current water level. The current water level then subtracts from the gap, causing it to get smaller.
The cycle now starts over again. The gap still adds to my motivation, yet since the gap is smaller the addition to my motivation is less. My motivation still adds to the extent to faucet is open, yet since my motivation is less the extent the faucet is open is less. The extent the faucet is open still adds to the water flow rate, yet since the extent the faucet is open is less the water flow rate is less. The water flow rate is still adds to the current water level, yet since the water flow rate is slower the rate at which it adds to the current water level is slower. And finally the current water level still subtracts from the gap, just not so quickly.
The cycle now repeats, again and again, until there is a balance
between the current water level and the desired water
level. When this state is reached the current water level
has subtracted from the gap until it is zero. With the
gap at zero there is no addition to my motivation
and no addition to the extent the faucet is open, which
means the faucet is now closed. With the faucet closed there is
no addition to the water flow rate, which means it is also
zero. All this means there is no more water entering the glass
so it doesn't overflow.
The structure continues to adjust until a balance is achieved between the current water level and the desired water level. The really important point to grasp here is that the actor is part of the structure. My motivation is part of the balancing loop, not an attribute of some external actor influencing the structure. This is a point often not clearly recognized and it is very important in terms of really understanding what's happening within the loop.