Answer:
This is a phrase from J. K. Rowling novel Harry Potter and the Philosopher's Stone (1997). It was said in the end of the book by Albus Dumbledore during yearly allocation of points to the houses of Hogwarts.
Here is why it a wise statement.
‘It takes a great deal of Bravery to stand up to your enemies’ because you stand up for challenge and your enemies usually do not mean good. For example, standing up against a bully in school takes bravery. Meanwhile, you do not have personal connection like friendship with your 'enemies'. You feelings towards them are more clear.
Meanwhile, ‘stand up to your friends’ takes more bravery, because you have positive relationships with them. You play together, spent free time, watch movies and help each other with homework. But one day you might disapprove of what your friend is doing, for example trying to smoke cigarettes. Than you have to stand up against your friend and take a risk of getting into a fight, hurt each others feelings and jeopardize your friendship. Such conflicts become much more personal than conflicts with your ‘enemies’. People often avoid standing up against friends just to avoid negative emotional experience.