Only fools rush in

 A good person is invincible, for they don't rush into contests in which they aren't the strongest. If you want their property, take it -- take also their staff, profession, and body. But you will never compel what they set out for, nor trap them in what they would avoid. For the only contest the good person enters is that of their own reasoned choice. How can such a person not be invincible?

-- Epictetus, Discourses, 3.6.5-7

"Some people think that 'choosing your battles' is weak or calculating. How could reducing the amount of times we fail or minimizing the number of needless injuries inflicted upon us be weak? How is that a bad thing? As the saying goes, discretion is the better part of valor. The Stoics call it reasoned choice. That means be reasonable! Think hard before choosing, and make yourself unbeatable. 

* Source: The Daily Stoic by Ryan Holiday and Stephen Hanselman