As a software engineer, I hate when I add a check for something "that will never happen" but that if happens is awful, and people complain.
A classic example: you need to get a user from a session, check against a database, and continue if they're signed in.
Then I add a simple if databaseUser.Username != form.Username and people will say "if that happens we've something worse wrong". Geez, something might be wrong and such double checking might provide to be useful.
On a smaller scale, bits flip due to cosmic rays and so on. Of course, there must be a limit where we stop, but people are used to actively avoid doing such "silly assertions" even for important steps.
¯\_(ツ)_/¯
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