"But I believe humans are fundamentally driven by 'three desires'. The first is 'material desire', the second is 'sexual desire', and finally the last desire holds more significance than the other two combined: 'the desire for knowledge'. Every human longs to be the smartest. Every human yearns to bask in the self-superiority of obtaining some nugget of knowledge not yet discovered by the rest of the humanity, and hoarding said knowledge for themselves!" 
(Mephisto Pheles - Ao No Exorcist, chapter 44)