A reinforcing loop is one in which an action produces a result which influences more of the same action thus resulting in growth or decline. The reinforcing loop is one of the two foundational structures of systems thinking, the other being the Balancing Loop. Consider the following example which describes a savings account.
Periodically the principal in the savings account interacts
with the interest rate and adds to the interest.
The interest rate in this example is assumed to be constant.
The interest then adds to the principal causing
it to increase. In the next period the cycle repeats, only now
the principal is greater than it was before so it's interaction
with the interest rate adds an even greater amount to the
interest. This larger interest then again adds to
the principal. The graph to the right above principal
shows the resultant growth of the principal.
Because of the manner in which this structure reinforces itself it generally produces an exponential growth or decline. This exponential change may be unnoticeable for a period of time until it reaches a certain threshold. The structure then seems to change very rapidly causing one to wonder how it began all at once, when in fact it really didn't. The growth just wasn't substantial enough to be noticed.
The reinforcing structure is one of the simplest structures and seldom ever occurs in isolation from additional influences. As was indicated above, nothing grows forever so there are extensions of this structure to be concerned about. The most prevalent extensions of the reinforcing structure are identified in the following areas of concern.
The following examples are intended to provide some specific instances in which a reinforcing structure is the primary structure.