Fi, being a static function, observes the person's own feelings and ethics towards other people and the form of expression that these observations take on are interpreted with emotions that than in the form of Ti, where they are thought, not felt. In many ways Fi becomes a function of imagining and reflecting on things, relationships, that are, were and could have been; this in no way makes Fi types “unrealistic;” even in the most idealistic of type, the INFj is quite capable of apprehending the static qualities of an object, Se, and unlike extraverts this function is not exercised on objects, preferential treatment goes to introversion.
Being a static function, Fi has the quiet, behind the scenes and internal action of connecting with others, feeling, establishing personal bonds and these things don't just arise out of no where. Take contact with someone of desire for a relationship; you may not know it or see it, but through regular contact with an individual, the Fi type will establish their own feelings of like and dislike, gradually, even if to the external world this process may seem sudden; we are just private people and don't let others see what's been brewing in the kettle. This static qualities allow us to “influence” someone less so inclined in the relationship department; we're able to say “we are compatible in these ways.” Since INFj, particularly are a positivist type, they are able to apprehend the positive qualities of the person first. Sure, there are negative parts to every person and relationship; we realize that. But, we'll leave that to people who are less trusting; we'll give them courage and strength to take bold step and leap in ways that will help open possibilities. In this way I am the possibility of relationships.
INFj influence the dynamic types with static information and when dynamics are “led” by our perceptions, relationships are built, tested, tried. It's nice to lead your dual with your conscious functions, it opens up their inner world, in profound ways. To maintain such bonds, of course the pairs have to understand that giving up control is essential. We can be influenced by the world around us to do things again our best nature.
ISFj are negativist types. Where if someone says..."I was going to wait 11 years to terminate my bad relationship, until my kids were grown."
And ISFj may say that "that will take way too long..." (the number is so large presents the negativist type something to worry about that may go wrong within that time frame, instead of the possibilities of positive qualities that things will result from that much time). That which is not filled is something to worry about
an INFj may say "the sooner the better..." That which has already filled is a source of relief.
Both may take the actions to terminate that relationship; however you can observe from the above, it's just a matter of how you look at the same thing, really; but that above, applied to EVERYTHING in life causes either relationship dynamics to go smoothly or in semi-dual relationships, not so smoothly.