presumptuousness, in general, is a problem of connecting stimuli and goals in the world to your own internal framework that helps you understand.
Fi users can project their own feelings into a person, based on their huge Fi framework, as they subjectively imagine, from the interior, what the other person's state of being, as umlau said, might be. that can be incredibly wrong. but sometimes it is extremely grounding, comforting, understanding, and accepting. depends whether you agree or disagree, i guess', in the particular context of the particular situation.
Fe users watch the exterior signs and the langauge o affect, the social grammar, and the cues of INTENTION to reconstruct a sense of the context of the scene itself. we're relying on our ability to map (Ni types) out the various constraints and prioritize them into a basic topology. we then guess the intention, much like umlau said. we can and do get this horribly wrong. however, just because we are seeing different forces operating than the Fi user doesn't mean that they alone have privilege to understand the situation. we may not get their feeling framework, but to say that we don't understand huge aspects of the situation is also similarly bullshit. yes, you have your own personal judgments, case histories, and inflected personal truths that give you unique shades. but there's a lot of consistency in life. this is where we get to the difference between left-brained and right-brained. this aspect of consistency. and this is why it's not accurate or even sane to bemoan the whole function or to say it's presumptuous. there's always a negotiation process. seymour's post really brilliantly brings this to light. the way an Fe user wants to help and the way the NATURAL TENDENCY of the person is to privilege the first function and react strongly when it is rejected. i had a class where my teacher was an istp who hated the fluidity, amorphousness, and lack of linear development of Ni. of course we battled. but finding a way to think with more than just the single function is a necessary step to development of consciousness. being able to integrate more from your second and third functions, while being able to at least moderately emulate other functions in order to get a sense of how the rest of the world's mind works, and most of all, to effectively communicate!!!
and yes, left-brained people are more broadcasting, shared social forms and representations, stereotypical (relying on shared symbols), language and culture based, and right brained people are more experientially driven, episodic memory, personal pragmatic reasoning, spatially aware, more in the moment, more focused on the difference and uniqueness of each experience. this makes right brained people more resistant to those shared understandings and more focused on their own unique experience/story.
if your long-term planning pre-frontal cortex executive function doesn't learn to integrate at least a bit of the non-dominant hemisphere into your CONSCIOUS reasoning process, you won't be a very good person. women supposedly have 40% more bandwidth at the corpus collosum between hemispheres. they usually develop earlier, whereas men's prefrontal cortext often doesn't fully come online until the late 20s. i know that when i have no access to interiors, i'm pretty shitty, and i don't like my life nearly as much. when i do, the world doesn't distort so wildly, and i have a story of my own to keep me going and give me greater resistant to both the climate and weather fluctuations of language, culture, social group, and specific scene.