Boundaries can be difficult to establish, for a variety of reasons: for some, the thought of boundaries is selfish while for others defining the boundaries is the challenge. Once defined and correctly implemented though, boundaries can assist in creating calm as expectations are managed for all involved. While it may appear the job is done, setting boundaries is not a once off task.
As relationships evolve, professional and personal, boundaries will need to be adjusted - either relaxed or made more stringent. Consider a friendship: it would be less acceptable to contact a new acquaintance late in the evening for a chat but more acceptable in a long-standing friendship where this boundary has become more relaxed. In a working relationship, regular lunch colleagues may need to create stricter boundaries around their lunch time if superiors feel the interaction is becoming inappropriate.
However, even where relationships are in a state of continuation, boundaries must be revisited. Humans are creatures of habit and we tend to slip back into old routines - sometimes despite our best efforts. Generally, this decline into the old and familiar is subtle and we are unaware of it, waking up one morning wondering how everything got so out of control. Again.