We internalize consciously or unconsciously patterns of thought and behavior, and the patterns that are useful to us, we call second nature, and those who are harmful to us we may call bloody roots.
We need to ask ourselves: How can we internalized good things and get rid of the bad ones?
First of all you need to critically exam yourself in order to determine what kind of bias made you incur in mistakes of judgment, and what are the reactions that you automated or that you can automate to improve your well-being and performance.
To get rid of negative thoughts and behaviors you to consciously replace them with rational analysis and productive actions. To do that, one must engage in the task that all trained philosopher engages constantly, an careful reflection about your past actions and the implications of them.
To make something become second nature, in other words, to turn nurture into nature, you need many hours of training and repetition.
To sum up, the hard task of distinguish the good from the bad in our minds is paramount to self improvement and to achieve greatness.