If you describe an idea or belief as a shibboleth, you mean that it is thought important by a group of people but may be old-fashioned or wrong.
[formal]
It is time to go beyond the shibboleth that conventional forces cannot deter.
shibboleth in British English
(ˈʃɪbəˌlɛθ)
noun
1.
a belief, principle, or practice which is commonly adhered to but which is thought by some people to be inappropriate or out of date
2.
a custom, phrase, or use of language that acts as a test of belonging to, or as a stumbling block to becoming a member of, a particular social class, profession, etc
Word origin
C14: from Hebrew, literally: ear of grain; the word is used in the Old Testament bythe Gileadites as a test word for the Ephraimites, who could not pronounce the soundsh
shibboleth in American English
(ˈʃɪbəˌlɛθ; ˈʃɪbələθ)
noun
1.
the test word used by the men of Gilead to distinguish the escaping Ephraimites, who pronounced the initial ( (ʃ) ) as (s): Judg. 12:4-6
2.
any test word or password
3.
any phrase, custom, etc. distinctive of a particular party, class, etc.
Word origin
ME sebolech, after LL(Ec) sciboleth < Heb shibolet, a stream: pres. meaning from the use of the word as a test word