The Dark Knight quote: “You either die a hero or live long enough to see yourself become the villain.”

Banksy pseudonymous England-based graffiti artist, political activist, and painter

Source: Wall and Piece

“The real problem with being around James was that he was always the hero. And what did that make you? Either the sidekick or the villain.”

Lev Grossman The Magicians

Source: The Magicians

“You learn eventually that, while there are no villains, there are no heroes either. And until you make the final discovery that there are only human beings, who are therefore all the more fascinating, you are liable to miss something.”

Paul Gallico (1897–1976) American writer and journalist

“Everything has an end, if only you live long enough to see it.”

H. Rider Haggard book King Solomon's Mines

Source: King Solomon's Mines (1885), Chapter 5, "Our March into the Desert"

“Learn from the mistakes of others. You can't live long enough to make them all yourself”

Eleanor Roosevelt (1884–1962) American politician, diplomat, and activist, and First Lady of the United States

Cited as a piece of anonymous folk-wisdom from the 1940s onwards https://books.google.com/books?id=iNkWAQAAMAAJ&dq=%22Learn+from+the+mistakes+of+others.+You+can%27t+live+long+enough+to+make+them+all+yourself%22&focus=searchwithinvolume&q=%22make+them+all+yourself%22. Not attributed to Eleanor Roosevelt until 2001 https://books.google.com/books?id=ctxi36FCi18C&pg=PA151&dq=%22Learn+from+the+mistakes+of+others%22+%22live+long%22+roosevelt&hl=en&sa=X&ved=0ahUKEwiI_sD5mqDLAhWIKGMKHb8HAZ0Q6AEIHTAA#v=onepage&q=%22Learn%20from%20the%20mistakes%20of%20others%22%20%22live%20long%22%20roosevelt&f=false.
Disputed

“You have to learn from the mistakes of others. You won't live long enough to make them all yourself.”

Hyman George Rickover (1900–1986) United States admiral

Variations of this quote have been attributed to a number of people, including Eleanor Roosevelt, Samuel Levenson, and Lao Tzu; there is no solid support for any such attribution.
Misattributed