Jealousy of brothers and sisters is very common in families, and is sometimes a cause, in later life, of homicidal mania as well as of less serious nervous disorders. ... At the birth of a new brother or sister, pains must be taken to prevent the others from imagining that they have become less important to their parents than they were. Wherever serious cases of jealousy occur, it will be found, I think, that these simple precepts have been disregarded.
Source: Bertrand Russell :Marriage and Morals, 1929
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