Why firewalls are like windshields

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A friend of mine walked into my office the other day, explaining that he had just acquired a router/firewall for his home network. He said that he had been examining the firewall logs and was surprised (as I was years ago) at the number of attacks and door knockers that continuously try to get in.

I explained to my friend that it doesn’t much matter who and what are trying to get in. To simplify the subject (something I excel in and have for years), I explained that a firewall is like an automobile windshield: yes it stops bugs, rain, rocks, and more, but we don’t need to examine each bug or rock or raindrop to determine its origin — it’s enough that the windshield does its job with little or no upkeep (save for a little Windex now and then). My friend really appreciated my analogy and thought it was great.