There are many predictions out there that say half the new marriages in the world will end in divorce. Because this is a prediction, it is not a number that can be counted on as a measure of successful marriages. Even if less than half a couple's friends are divorced, it does not mean their marriage will end that way. Their marriage is just as likely to suffer from a temporary separation, one partner dying prematurely, or having a happy and successful marriage. The statistics attempt to predict the future, not the current state of marriages.
No matter what statistics say, they are often just an average. A couple may get married, never consider divorce at all and live happily ever after. All of their married friends and family may have the same happy lives. Statistics affect a group, not individuals, and cannot predict how any individual marriage will fare over a lifetime.