I heard that tradition is when you can't remember when it started or you prefer not to. E P Thompson in Customs in Common discussed how 'tradition' was often used to assert 'ancient rights' by ancient rites.

I am interested in how quickly appropriation or creation can become entrenched enough to be thought of as tradition.   I've talked to quite a few people this year at our local Sheffield Carols who have adopted them around the country using recordings and books as well as directly from singers.

Should people invent their own customs rather than seek instant legitimacy or is imitation how it all spread anyway?