A quote from Christopher Nolan's The Dark Knight by the character Harvey Dent in reference to Julius
Caesar and Batman. Repeated by Batman at the end of the film.
There are several possible meanings:
1. Absolute power eventually corrupts (as in the
case of Julius Caesar).
2. Being consistently heroic is difficult if not impossible, circumstances will eventually push you towards villainy (as in the
case of Harvey Dent and Batman).
3. Public
opinion can easily change and will eventually change. Many people have the tendency find faults even when there are none. It can also be easily manipulated. You might adhere to your
code despite 1. and 2., you can still be painted as a villain by your enemies (as in the
case of what Joker did to Batman).
4. Villainy and Heroism are relative and not absolute. "Good" will change with
time. Different people have different concepts of "good" (the actions of Julius Caesar can be judged very differently by different people throughout the different ages). In many situations, the
line between the two concepts can be very blurry (following the law versus vigilantism).