Quote:

One spare for 2 canoes?  That sounds like saying, "I have seat belts in my other car, so I'm covered."

No it is not.  If you are in the second car and it crashes, the seat belts in the first car do you no good.  If   you lose a paddle in the second canoe, the paddle in the first canoe is as useful as having the spare paddle in the second canoe.

A paddle is similar to many other "vital" items we take on trips: orienting devices, stoves, flashlights, paddles, canoes, tents.  We assess the liklihood and severity of failure, the weight, etc; and make a decision of how many (if any) backups to bring.