Simplify the following text for a Grade 8 native English-speaking person.
Original: Rules of etiquette are usually unwritten , but aspects of etiquette have been codified from time to time .
Simplified: It is usually unwritten , but it may be put in written form . Because they are a product of the society 's culture and history , the rules of etiquette are very different from time to time , and from one place and social group to another .