Among other things, Nine-ness is a **selfishness** about maintaining my own inner sanctum of stillness and calm, and since I can "smell needs from a 100 miles away", I continually avoid being around people... in numerous ways.
Me, personally, I MUST have MANY hours of alone time. I'm 53 years old, live alone, never been married, made sure to never produce children, cannot imagine why anyone would ever have children or a spouse. Why would you ruin your life like that? [Note to future self: Next time, insert a smiley-face emoji at this point in the conversation so that the people know you're not a sociopath; you're actually a very kind and compassionate man, aren't you???]
On some level, I see 9-ness as hypersensitivity disorder -- I'm absorbing people at the level of my body, I'm sensing *too much* about them, I'm in some danger of being 'possessed,' so I'm also, especially as self-pres dom, making sure to say 'No' to all of that, because of the degree to which I can be 'taken.'
As a Gut type, very deep down, 9 is highly invested in maintaining autonomy/independence. The 9s who are more clearly 'giving themselves away' are somewhat engaging a 'management system' that (unconsciously) appears to them, at the onset of each connection or interaction, as 'serviceable enough' for the protection and soothing of the 9's own inner sanctum. This is the 9 motif of "If everyone around me is ok, then I'm ok."
I'm purposely, for the sake of some brevity, leaving out the 'human heart' element in the above (my heart, other 9's hearts), but of course all the above is complicated by the fact that I'm (me personally) also being affected by others often at the level of Feeling, compassion, empathy. Nonverbal emotional intelligence and insight is often an area of mastery for 9s, and the people in a given 9's life may have no idea about the depth to which the 9 is getting saturated by the emotional weight of the other person/people, an absorption which might often have its start in the heart and emotions, or some combination of heart and body-sensing of emotional content.
Again though, it can't be overstated ... a main concern with self-pres 9... the self-pres instinct's sensitivity and capacity for alarm and watchfulness about "what's happening to ME, RIGHT NOW", which can often amplify the Gut center's concern around boundary encroachment and sustained autonomy.
A given situation with another person has the potential to register, resonate, and reverberate loudly, though nonverbally, throughout the body, and can be experienced as something like a mortal threat, instinctually. Of course, ultimately (I mean, like, ultimately-ultimately), this concern, in most cases, is all an illusion -- there's no real mortal threat and there never was -- but try telling that to an animal instinct that has no verbal capacity.
Self-pres is also looking into the future, toward 'possible future time & energy expenditure' as it relates to this or that person or group situation. And since, as a 9, I so inadvertently tend to saturate with other people's stuff ('smell them 100 miles away' <--- By the way, imagine what that means in terms of what happens *up close* with you and other people), I *must* do 'No' or develop a capacity for 'No'.... otherwise the sacrosanct inner sanctum might imagine or sense that it's in danger of merging with the mess and perpetual agitation that is this other person or these other several human beings, a foundational shock that would never stop reverberating, making waves in the silent ripple-less pool of the sanctum.