No doubt I'm far from the only person to have realised this ... but pass it on for those who are beginning their research.
An incident from the past is related as happening to, e.g. a sibling, parent, cousin, uncle, aunt ... the same incident is related to the next generation without any adjustment of the relationship of the principal person in the story. That generation again relates the incident to the next, etc. Thus the event described was probably real (as I have often discovered), but the generation, actors, time, place, character, are inexact. (The then large size of families also complicates matters, since a cousin, uncle, aunt, could be older than a person in the generation above them.)
An example from my own family:
After Sunday lunch c.1955 I managed to get the parents discussing their ancestors (I was already hooked on fh). Eventually came the remark from Mum - that she'd had an "old Aunt" (by which was meant a person of her grandmother's generation) "name of Doolinon, French I think" - without which I could never have been sure, in 2014, of this (inverted) tree:
<—Millie (Amelia Maud) TAYLOR (m. TILBURY)
<—Launcelot TAYLOR (m. HENLEY)
<—James TAYLOR m. Frances Mary WATERMAN
<—Frances' father: George WATERMAN
<—George's father: William WATERMAN
William's wife: Mary Ann BURWOOD
<—Mary Ann's father: David BURWOOD
David's wife: Elizabeth DULIGNON (of Huguenot extraction)
That is, not two generations above her own, but five!!!
May I invite you to harvest your family's mythology carefully, you never know what golden nuggets could be hidden therein. (Discreetly "liquified" family anecdote evenings, recorded?)
Another example from the same lady, but of a different kind, was related at the kitchen sink when we were discussing the previous evening's Prom. Thus I eventually discovered that the French musician Louis Jullien was responsible for bringing the Promenade Concert - and "serious" music for the masses - to the UK, to many other countries - and the symphony orchestra to the United States. Sadly for me, several years of my research were stolen from my computer, but I hope nonetheless to succeed in re-assembling, publishing it all on my website. (Unfortunately that's another sometime reality of fh: people who have no interest in doing the research, sharing, but are out for their own glory and advantage.) The clue I received for Jullien was, c.1953, that her ancestors had gone to the Proms at the Zoo. Asking whether that was at Regent's Park, the reply came "no, the other zoo" - "which other zoo?" - "the one south of the Thames". Doubting I said, "but there isn't one" which was followed by "no, but there was" - and she would say no more. It took another 50 years, the Internet, Google Books, old newspapers online, France's National Library online, for me to discover Jullien, Frederick Strange, the Royal Surrey Gardens, the largest Music-hall in Europe - and the dreadful accident which occurred there; its occupation by St. Thomas's Hospital; and the sad end to Jullien's life.
Whether or not her ancestors - in this context again the Watermans - paid any entry fees, I'm not sure, since in view of their proximity to the Gardens, and the volume of sound Jullien's efforts disseminated, they might well have been able to listen at home ... without benefit of radio ....
Parenthesis: it was while exploring Frederick Strange's activities that I read of ballerina Giovannina Pitteri at the Alhambra (from La Scala, Milan, via the Paris Opera Ballet), trained in the Vestris style and an admirer of Marie Taglioni. Strange was producing ballet - in its then form - when it could not be seen elsewhere in London. A forerunner of Sadlers Wells.
From my own experience, probably rarely a secret for all the family! Those who had an interest in keeping quiet, may have done so, but the rest of their family were often more loquacious in private. Thus it's sometimes possible to learn about past events from the wider circle of relations; they may hold the clues without knowing the cause: up to the family historian to put 2 + 2 together, in the hope of not making 25.
... which may now cause puzzlement, stress, unhappiness, more than at the time. A modification to the Children's Act, in 1939 and in preparation for war, which guaranteed eternal secrecy regarding any change of identity of children adopted in a simplified manner when no family of their own remained able to shelter them. The purpose was the continuity and survival of the nation, which could only be in the care for, and education of, its children. This applied to many, many children. Even in recent time, according to people of my own generation (I'm 72), the Registrar General has refused to give a copy of an original entry of birth to a person who remembers their (previous) name, the place where they lived, their family .... So far as I know, the Registrar General solely may give such permission. Many children were too young to remember for long, and even if they knew more or less where they had lived, those houses, streets, were unidentifiable: nameless, numberless, piles of rubble still into the 1950s. (An aunt took me on a tour of such parts of London when I was 11.)
In the early post-war period the social, recreational, use of DNA testing was unthinkable. Now the results may cause perplexity and even destabilisation to those who discover their ancestors to be families of whom they know nothing.
(Personal opinion: it's high time the secrecy was lifted, that there be public discussion of past events, and that those families who assumed responsibility for homeless children be respected for their efforts, but that the families who were killed, or whose circumstances postwar made it impossible for them to take back their children, be also acknowledged for their sacrifice - and that we may trace both family lines with love and remembrance. Let the listing be public, as with most - but not all - BMD.)
My thanks to NickS for this link to the story of evacuees sent to Canada: