To have manners is either instilled, appropriated or influenced by traditions. But sometimes it is hard to take the same part in a group like other members with other standards.
To avoid this situation or to exclude other persons and let them feel uncomfortable at the dining table
“Don't let it to a habit” makes it easier. It helps to hush up the possible differences between all members.
With using “Don't let it to habit” there is no chance to see wrong behaviour, because everyone has the same standard.
