We find it easier to rejoice with those who rejoice than to weep with those who weep. Let's face it, in most cases those who rejoice are so eager to rejoice they'll spend their own money to invite you to rejoice with them. I've been invited to just enough weddings here that I am not idly saying this, nor am I saying for a second I wasn't fully of genuine joy to be at the weddings I've attended in the last two years. Those weddings were the high points of my social life in the last few years, no kidding.
But Proverbs says that even in laughter there is sadness and the end of joy is grief. The joy of the wedding day is real and should be celebrated and cherished because the unknown day may come when grief and sickness and, finally, death arrive. The day is not unknown because there will never be grief, sickness or death but because we do not know when that day comes.