The posture of the Knight of Cups implies that of a messenger, so it comes as little surprise that he often manifests as a bearer of news. He represents invitations, messages of love and proposals of marriage. In addition to the physical sources of information, the Knight of Cups can also represent wisdom that comes from your dreams to help you surmount obstacles in your life at the moment. Sometimes this card can represent the start of a relationship, but in this case if often serves to warn one or both partners. It shows daydreaming and idealism, and it can highlight relationships in which one partner is placed on an unfair pedestal.
Given that, it's easy to see that the person represented by the Knight of Cups will be a dreamer, one who is prone to wild ideas and flights of fancy. His wild imagination puts a bit of a spark in any relationship he's involved in, and he always seems to be in a relationship of some kind because he's a born romantic - and a hopeless flirt. Beneath his calm exterior he is a man of intense passion, though he generally diverts this passion towards reaching his goals and making his dreams come true. His is an idealistic view of life that is scorned by the active and despised by the realist. Inversely, he has no tolerance for people who cannot believe in their dreams.
When you are getting too wrapped up in your dreams, or when your idealism is starting to blind you, the Knight of Cups will appear as a warning. When you have no dreams and your view is too realistic, he will appear to show you what you are missing out on! As the Knight of the suit of Water, his view of life is fairly moderate in the majority of cases. Follow your dreams, but do not let them become an obsession. Develop your imagination, and let it guide you, but never let it rule you or lead you to ruin. Show love but do not go overboard and become committed to something you cannot handle. Make sure you are in control of your life, and your dreams.
What is my passion? Why, Roller Derby, of course! I guess you could call it following my dream but don't think I'm obsessed with it. Not yet, anyway!