"It is the constant fault and inseparable evil quality of ambition, that it never looks behind it."
- Seneca

"Ambition is so powerful a passion in the human breast, that however high we reach we are never satisfied."
- Niccolo Machiavelli

"Ambition does not constitute a character flaw which leads to the dishonesty and dissatisfaction bemoaned by critics throughout the ages.  The results showed that under the model developed and tested, ambition does not make one miserable nor does it create feelings of unquenchable desires for outcomes beyond stretch goals.  Instead, ambition, an habitual level of striving for or desiring accomplishment in life situations associated with important human capital-related outcomes, correlates with educational attainment and educational prestige."
- From Ambition: An Important Character Trait And Predictor of Positive Life Outcomes by Dan DeFoe
http://www.psycholawlogy.com/2013/03/16/ambition-an-important-trait-and-predictor/