A man who stays long in our American political life, if he has in his soul the generous desire to do effective service for great causes, inevitably grows to regard himself merely as one of many instruments, all of which it may be necessary to use, one at one time, one at another, in achieving the triumph of those causes
 Theodore Roosevelt, Theodore Roosevelt; an Autobiography (1913). copy citation

Context

“To play the demagogue for purposes of self-interest is a cardinal sin against the people in a democracy, exactly as to play the courtier for such purposes is a cardinal sin against the people under other forms of government. A man who stays long in our American political life, if he has in his soul the generous desire to do effective service for great causes, inevitably grows to regard himself merely as one of many instruments, all of which it may be necessary to use, one at one time, one at another, in achieving the triumph of those causes; and whenever the usefulness of any one has been exhausted, it is to be thrown aside. If such a man is wise, he will gladly do the thing that is next, when the time and the need come together, without asking what the future holds for him.” source