Nine at the beginning is a reading about timing rather than about strictness. The line shows restrictions established in the household and says that cause for regret disappears. A querent drawing it is usually at the start of something shared, a home, a partnership, a working arrangement whose terms nobody has yet felt any need to state, and the counsel is to state them now, while stating them is uncontroversial.
The practical weight sits on what the line does not describe. There is no dispute in it, no offender and no grievance being answered, and that absence is the condition under which a boundary can be set without being received as an accusation. A reading arriving here is being told that it holds an advantage which will not survive the first real disagreement, and that the advantage is worth spending immediately rather than saving.
When the line changes, the lower trigram Li becomes Gen and the figure becomes Development, King Wen 53, the gradual advance the classic illustrates through a bird moving stage by stage and refuses to let hurry. That destination explains what the early rule is for. Order established at the outset is what makes slow growth possible afterwards, and an arrangement that has to renegotiate its own terms at every stage never gets far enough to experience the patient progress this figure describes.