MEDIUMSHIP - OBSESSION: IN THE WORKING MEDIUM
Kardec warns, "Obsession, as we have said, is one of the worst stumbling-blocks of medianimity, as it is also one of the most frequent; we should, therefore, do our utmost to combat it, for, besides the personal annoyances to which it may lead, it is an absolute bar to the reception of truthful communications. Obsession being always the result of restraint, and restraint never being exercised by a good spirit, it follows that every communication transmitted by an obsessed medium is vitiated in its origin, and is, therefore, undeserving of confidence."
For additional observations and explanations regarding obsession in mediums, please see chapter XXIII in "The Mediums' Book".
Kardec, Allan. "Obsession." The Mediums' Book. 2nd ed (1st edition FEB). Trans. Anna Blackwell (translated 1876). Ed. Livraria Espírita Allan Kardec. Brasilia-DF, Brazil: Federação Espírita Brasileira [Brazilian Spiritist Federation}.1986. 277-282.