some of the interesting concepts that i found in machiavelli's "the prince":

"one should never allow chaos to develop in order to avoid going to war"

"the arms of another man either slide off your back, or weigh you down, or tie you up"

"one can generall say this about men: that they are ungrateful, fickle, simulators, and deceivers, avoiders of dangers, greedy for gain;"

"fortune is a woman, and it is necessary, in order to keep her down, to beat her and struggle with her. and it is seen that she more oftern allows herself to be taken over by men who are impetuous than by those who make cold advances; and then, being a woman, she is always the friend of young men for they are less cautious, more aggressive, and they command her with more audacity."

"ingenuity over rage" (this actually part of a quote from petrarch)