nittel nacht was developed as a means of self-preservation. it was commonplace for pogroms to occur around the christmas holiday when everyone was feeling "christlike". christian activities would include harassing jews in the streets, breaking into jewish business, and sometimes straight-up murdering people.  another reason for nittle nacht exists is based in the concept of marit ayin (appearance to the eye) which states that jews shjould avoid situations or actions that appear to violate jewish law, such as eating at a non-kosher restaurant, even if what you are ordering complies with kashrut.
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