This structure is a variation of the standard balancing loop. The variation being that there are one or more delays in the structure which are responsible for producing a very different behavior pattern than with the standard balancing loop.
The desired state interacts with the current state to produce a gap. The desired state is considered to be fixed during this consideration. The gap created by the difference between the desired state and the current state is really the motivation for action, and the larger the gap the grater the tendency to produce action. The action taken then adds to the current state. The current state subtracts from the gap, thus reducing it. When the action succeeds in moving the current state to a point where it is equal to the desired state the gap is reduced to zero and there is no more motivation for action.
Delays within this structure could exists between the time the action is taken and the time current state changes, or between the time current state actually changes and the time it is realized in order to affect the extent of the action being taken. A delay at either location will have essentially the same affect. The affect being that the action will continue to add to the current state at a level above what it should. This is essentially an overreaction which will tend to drive the current state beyond the desired state and the gap will go negative. The structure's reaction to this is to run in reverse, if this is possible for the particular instance described by the structure. The delay may be such as to cause overreaction in the opposite direction to move the current state below the current state. With a sufficient delay the structure will result in larger and larger oscillations over time.