Social psychologists point to the importance of a belief in justice as a motivating factor for the individual. The U15 complex concerns laughter as an appropriate response to rampant injustice, recalling physicist Niels Bohr's comment that there are some things so serious you just have to laugh at them. In folklore, on those occasions when justice is realized, it tends to be of the poetic sort rather than the judicial. Such examples of justice are cross-referenced under "Murder Will Out," which is found under Chance and Fate. In the days of King John of Acre a bell was hung for anyone to ring who had received a great wrong, whereupon the king would call together the wise men appointed for this purpose, in order that justice might be done. A promise that temporal injustice will be recompensed in an afterlife, so that the "last shall be first," is a central feature of many religious belief systems.