A philosophical concept and practical testing principle holding that to know a thing well, one must know its limits. In harsh environments like Arrakis, Amtal demanded that every object upon which survival depended be tested to destruction. For the Fremen, Amtal became religious ritual: life on Arrakis was the ultimate test in which all things were known by how they were destroyed. Only Shai-Hulud, the indestructible sandworm, appeared exempt. The principle extended to people as well as objects, with every Fremen subject to continuous testing throughout their lives.