if not a misattribution, sounds suspiciously similar to this line by e.e. cummings:

To be nobody but

yourself in a world

which is doing its best day and night to make you like

everybody else means to fight the hardest battle

which any human being can fight and never stop fighting

(and unless my memory is playing tricks on me, it appears that the goodreads site from which i copied the above presumes to know better than mr cummings and has replaced the word "man" with --human being--)