Decay is inevitable, but its rate is heavily dependent on the amount of resistance it faces. Too much will cause excessive wear, but too little will result in atrophy. As with our minds and our bodies, our mental models and constructs must regularly be put under sufficient stress to remain sharp and relevant.
The simplest way to this is through open discussion, preferably with an opposing viewpoint. It is in these trusting places where growth becomes possible—where we feel the safety net beneath us to venture beyond the comforts and conveniences of our thoughts and ideas.
To avoid discussion is often to avoid truth. Similarly, actively pursuing truth outside ourselves, even if undirected, will put us in greater positions of exposure to the moments that can change our life. If the goal is truth, there should be no fear of the fire that purifies all.