Keeping a spare sounds sensible until every cupboard is full of spares

An extra cable, a spare umbrella and a backup container can each seem like a practical idea. Together they take space, and finding the right one later becomes its own task. Whether a spare is useful depends on how often the item is needed, how easily it can be replaced and who shares the storage. How do people decide what deserves a backup? Interested in ordinary household trade-offs, including items that are easy to forget about until another almost-identical one arrives.