Forgetting to order the gravel

During our conversation on Thursday, my therapist WC introduced me to yet another particularly poignant illustration, this one about the fragility of carefully and artfully rectified mental stability: you have to remember to order in the gravel.
If one pictures thoughts as being like currents of water coursing through the brain, then thought patterns are like river valleys, their streams carving themselves ever more profoundly decade upon decade.
As comfortable as the water becomes, following its familiar course, as do one's thoughts - happy to pursue the precise and comfortable path which has been laid out for them. The subsequent liquid is increasingly more and more likely to follow the path laid out by the preceding flow. The greatest river valleys all started out one day as small streams, grown with the passage of time and with the predictable assurance of the path of least resistance.
The point he makes is clear: the temptation in such a project is to focus on the obvious work: digging the new chanel and diverting the flow. The durability of the job however depends on the backfilling: you must remember to order in the gravel, and fill all those low-lying areas whither the stream is so eager to flow.
I forgot to order in the gravel, and found my mental flow straying from the newly-constructed chanel and eating away at the banks of the old, familiar stream. It was time to backfill that valley, and to remember to monitor it for future erosion.