We will get number of messages to our Whatsapp account and it has given blue ticks option also which helps to know status of their sent messages. They will get to know about if you read their message or not by using blue tick option. Sometimes we are not intreasted to show them that you have not seen message even if you read them. Here is an option on messenger that we can disable blue tick on whatsapp so that the sender will not get blue tick symbol