What does it mean if you don't write on the lines?

Answer 1

It means that you choose your own path, rather than using guidance to seek your path. The lines on a page, here, are compared to guidance given to you, perhaps in the form of senior advise, that you decide to neglect, hence not writing on the lines and not following them.

I wouldn't advise that you take it literally, as not writing on the lines literally is not a good idea, like if you're filling in an application form, anything to be scanned by a computer or indeed a health form or government census. This could potentially be detrimental to your health or cost you your job, or money.

Reading between the lines is not a related phrase, though it may be confused. Reading between the lines refers to not taking the content literally, but to seek a solution through lateral thinking.

Answer 2

Writing off the lines typically means that a person's handwriting is not following the designated spaces for writing. This could indicate a lack of attention to detail, carelessness, or a disregard for rules.