If you have not even a little imagination, you are simply a brute. So you must not lower your ideal, neither are you to lose sight of practicality. We must avoid the two extremes.... You must try to combine in your life immense idealism with immense practicality.
When you know both yourself as well as your competition, you are never in danger. To know yourself and not others, gives you half a chance of winning. Knowing neither yourself or your competition puts you in a position to lose.