It does not mean that there is no reason to strive for goals because everything comes to an end anyway. It does not mean avoiding the things you're passionate about or believe in because they are temporary. It means that when you have fought for your beliefs as hard as you can, when you have given your heart to a cause or person to the best of your ability and with integrity, and things change in anyway, be grateful everyday that the good is in your life and accept the negative and the pain for it will pass. Good will return and you can go back to being grateful for it. Pain will come and know that there is good on its way.
That's what I believe in. This is especially true when fighting for something or someone you believe in. Understanding that there might be pain and difficulty along way and knowing it will pass, allowing for the greater goal to bring good and happiness with it.