It´s not a rule, it basically is a principle in a form that´s easy to remember. It clearly needs adaptation to the personal way of life. I think you got the spirit of it very well.
I do not mind to finish a task when it takes staying after my usual office hours. However when I decide to call it a day, I do so. I do not keep chewing it over when I am out of office. The results benefit from it.
A coworker who used to allow work life to take over his personal life entered a vicious circle. His performance dropped rapidly causing him to have to sacrifice even more of his personal life. Eventually he ended up with almost a year of treatment for a burn out syndrome.