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The canonical quote is that "we lock our doors to keep honest people honest."

Practically, we cannot guarantee the security of our locks, or homes, or cars/bikes, etc. But we erect barriers to help enforce societal norms regarding security and privacy. These can be explicit measures such as door locks and deadbolts, and more holistic things like living in a good neighborhood, meeting your neighbors, preempting the broken windows effect, etc.

The only guarantee, in terms of home security, is a great insurance policy with riders for your major possessions.