Where was I wrong?

If you'd asked me twenty years ago whether it was feasible to run a telephone system without a telephone book I would have said no. Historically, the telephone book came along within a few years of the telephone, and it would have seemed to me axiomatic that telephones and telephone books were something like cars and highways - the individual benefit of one rested on the systematic commonalities of the other.

And I was apparently wrong, because the mobile phone has moved into dominance - may eventually move into sole practice - without phone books. There is no mobile phone book - listing your mp number anywhere is optional. and this is not a barrier.

I was obviously misguided, but still I can't see why.