“A line indicates a limit, saying, “That’s as far as you get.”
To maintain that boundary means to maintain the same familiarity, and it means that one will respect the universe that it outlines by abiding by its rules and maintaining the relationships existing in it as they are. This also means that, if one were to never cross that line, one would never experience the world, rules, and relationships outside of the currently established boundaries. If one wishes for a new relationship… if one wishes for love… one must cross the line. If one were to not cross the line… that line would demarcate the limit of how far you and that person can go.
Of course, there are some lines in this world that should never be crossed.”
— from Reply 1988, Episode 9: What It Means to Cross the Line