Most symbols or analogies break down at some point.
This is true with our sand and three cords ceremonies. For example, technically we could painstakingly separate the sands, and our "cord of three strands" is actually three cords of many stands braided together. It is also true with the unity candle--it gets blown out right after the ceremony.
Being the logic-loving person that I am, I had to choose not to let these and other little technicalities stop me from using these ceremonies which only roughly symbolize the amazing, God-enabled gracious uniting that took place as we became man and wife, as we became one. They are after all only symbols.
Another reason we choose these tangible symbols is that we can use them to share freely with our Taiwanese friends and family our belief that our marriage is not just between Lawrance and myself. As we explain our sand that sits in our living room or the cords that will one day hang in our dinning room, we get to share the gospel.
This thought alone put a stop to me wanting to argue myself out of using symbols that break down and aren't one hundred percent "foolproof."
Just thought I'd put in my two-cents now for any logic-loving naysayers that might or might not be out there. :)