@ Thierry Gourvénec
Wikipedia(en) / Leon Festinger
Festinger also later described the increased conviction and
proselytizing by cult members after disconfirmation as a specific
instantiation of cognitive dissonance (i.e., increased proselytizing
reduced dissonance by producing the knowledge that others also accepted
their beliefs) and its application to understanding complex, mass
phenomena.[55]
The observations reported in When Prophecy Fails were the first experimental evidence for belief perseverance