It is important for citizens to know the bill of rights, because the bill tells each citizens their rights (literally), and they will be able to know of what they can do and cannot during a event, and what is "constitutional". For example, they will know that they 'have the right to remain silent'. If they didn't know this, they would be forced to speak what they wouldn't want to say. However, if they know it, other people cannot force them to say what they don't want to say, because all citizens are protected.
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