Fear is the main source of superstition, and one of the main sources of cruelty. To conquer fear is the beginning of wisdom. Bertrand Russell
Questions that pertain to the foundations of mathematics, although treated by many in recent times, still lack a satisfactory solution. Ambiguity of language is philosophy's main source of problems. That is why it is of the utmost importance to examine attentively the very words we use. Giuseppe Peano
The main source of psychopathic diseases is the fundamental instinct of fear with its manifestations, the feeling of anxiety, anguish, and worry. Boris Sidis
My main source for faith-based stuff is mostly the Bible, and a childhood with a much, much higher-than-median exposure to theological thought. Jim Butcher
The state can be and has often been in the course of history the main source of mischief and disaster. Ludwig von Mises
In Shakespearean tragedy the main source of the convulsion which produces suffering and death is never good: good contributes to this convulsion only from its tragic implication with its opposite in one and the same character. Andrew Coyle Bradley