We keep a number of oil lamps around the house, both for emergency lighting and (in winter) some warm atmosphere.
But accidents happen. The other day Younger Daughter was pulling on her coat as she walked past the lamps, and the edge of her sleeve caught both lamps and tumbled them to the floor. Amazingly the lamp bases (full of kerosene) didn't break, but one of the globes did. Shattered, in fact.
Beyond the distraction of cleaning up the glass shards, this left me with one lamp temporarily unusable. No biggee right now, but it would be a different story if we were depending on them for light.
I wasn't worried because I keep extra globes packed in old liquor boxes (which have dividers). Every time I go into a thrift store, I scour their glass aisle for oil lamp globes and pick them up as I find them.
Within minutes both lamps were usable once more. But this minor, trivial incident underscored something important: in a prepared lifestyle, duplicates are always a good idea. The extra glass globes I keep on hand is the lighting equivalent of a deep larder.
Remember the old Rule of Three? Two is one and one is none...