Diclaimer: This post is my interpretation of two of melodramatic movies. Both of them with completely different story lines and one can go on to say they convey entirely opposite meanings. Also, I have no authority on the subject, but what the heck.
Serendipity is where John Cusack and Kate Beckinsale meet on a christmas eve,have precious few hours and feel a connection between them. He wants her number but she insists that, if fate wanted them to meet again, they would. So he writes his name and phone number on a 5 dollar bill and gives it away and she writes her name and phone on a book and agrees to sell it in a book shop. The rest of the movie is about how they meet again after few (predictable) twists and turns.
500 Days of Summer is about Joseph Gordon-Levitt who falls in love with Zooey Deschanel and believes she is his soul-mate, though she lets him know up front that she doesn’t really believe in relationships. When she breaks up with him and marries some one else, it does a real number on him. Eventually he lets her go, after he realises there is no such thing as destiny or soul-mate, instead everything is just coincidence.
As I mentioned earlier, the films are entirely contrasting in their message. While the first one is about how fate is always trying to get you to your significant other, the latter is that there is no cosmic significance to one’s love life. There is one common point though. Destiny or no destiny, what one gets is only the sum of how much passion he has towards that. The sum of all your actions decides where you go, or in this case, whom you get to live with. Life is short. Moments that you can remember are much shorter. What I am trying to get at it is, go have your moments. If you fail, that is okay. You can crib about it later. It will get you a real nice story to tell your friends at least.