An attempt has been made to explain the advantages of the behavior of prestressed concrete reactor vessels in a simple, brief, and qualitative form. In contrast to the property of spontaneous propagation of brittle fracture in massive steel plates, the failure of one prestressing wire or tendon does not propagate into the adjacent wires or tendons. The pressure-deflection curve does not end by a sudden failure, but the decrease of slope on approach to failure is gradual and even after formation of through cracks the vessel would close if depressurized. The energy absorption capability in post-elastic deformation is much higher than that of a steel vessel which could fail by brittle fracture. A weak part is the top closure slab, but if it is designed sufficiently thick to assure that a separation of a conical segment does not create a hole through the slab, and if much higher safety factors are used than those for the barrel sections, a very favorable failure behavior is assured. Comparison of the behavior of concrete and steel vessels in accidental exposure to high temperature and the role of moisture in concrete deserve further investigation.