Answer:
You row in one while you float.
I have joy in bringing two together, but darning my existence! My life hangs by a thread, filled with ups, downs and resistance!
There is a man in a 4 story building. He jumps out of the window and is unharmed. He used no padding, and had no harm done. How?
It is a form of plastic money.
What's always coming, but never arrives?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.