As a general rule, the First Amendment entitles you to write or say pretty much anything you want as long as what you write or say is true. But that rule has some exceptions. For example, if you are a former government official, you cannot disclose state secrets. Likewise, if you signed a confidentiality agreement with a former employer, you cannot disclose proprietary information covered by the agreement.
Furthermore, even if you are absolutely convinced that what you are writing is true and you don't care whether the people about whom you are writing will be upset by your words, you should consider whether some of these persons may be likely to accuse you of defamation and tie you up in costly litigation. That is why newspapers and television stations routinely have attorneys knowledgeable about libel law screen their story ideas and why you may wish to do so as well, especially if you expect your book to reach a sizable audience.
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