You cease to live fully when regret takes the place of your dreams.
There's two topics in the forums that have just recently been created: one titled 'Regret' and one titled 'Dreams'. The first is about what you -didn't- do that you regret, and the second is about the weird nighttime dreams that people have. But even though they don't really fit the quote, it's what came to mind when I first saw both of them together.
I regret many things, but most of them I can't do anything about now, and most don't relate to my current dreams. I don't fully agree with the quote above; I personally believe that you can regret and also keep your dreams at the same time, and be a more complete person in the process.
Life isn't about being happy. It isn't about the good things, the dreams, the highs and ups. Life is about being happy and unhappy, about both the good and bad things, the dreams and the regrets, the highs and lows, the downs as well as the ups. Life isn't about one or the other, it's about everything; black or white or gray.
Don't let either your dreams or your regrets disappear, because both of those make up the person you are. Neither on their own are you.