@Jawz, clear your inbox so I can reply to you!
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A lot of stuff people associate with 4w5s is just 4 stuff in general. Heavy introversion, drawn to intellectualism, being withdrawn, having a dark/morbid side, etc, that is just typical 4 stuff.
On the other hand, a misconception I've read in profiles is that 4w3s are more image focused...this may be slightly true because they have a double image type, so to speak, but I see that 3 aspect as manifesting in their social image more. The cultivation of a unique visual image can be a common 4 thing in general (ie. self-expression via their dress/grooming), and a 4w5 may put considerable effort into their visual image too. I mean, consider many famous people who are typed 4w5; they often have very crafted, unique styles. I say this because I'm a typical 4 in being something of an aesthete and creating an identity
partially via my appearance. I've seen this idea that 4w5s are disinterested in their own visual image & may just cop some black & minimalistic garb, but I suspect this is more likely 5w4 (if we're making style generalizations). That's really the only aspect of 4w3s that I relate to more than 4w5, and it seems inaccurate at that.
When I read the 4w3 descriptions, I found it more appealing though. It sounded like someone who was considerably more functional in life. My first reaction was, well, to be envious. I felt like I didn't have those qualities, like I was more cursed than these 4s who have this 3 "advantage". The 4w5 descriptions can be very dark....they often end with this description of a 4w5 descending into this mental misery of dark feelings & hopelessness. Whereas 4w3s get a slightly lighter "they can do well for a bit before self-sabotaging" slant.
I still feel like I don't have those 3 qualities, but I see the 4w5 "fate" as less dire. I related heavily to the 5 mindset, so much so I almost considered for it my type (but I am clearly a 4). The need to understand things to feel more equipped in life & fear of being overwhelmed by external forces is big with me. I feel like the world takes a lot, and I don't have enough to give.
To me, the 3 vs 4 wing in a nutshell is a matter of what markers the type uses to affirm their uniqueness, their personal significance, to ease feeling defective. The 3 wing brings a tendency to use external markers in addition to the 4 inner ideals & to accomplish things in reality - the person wants to do things which assert they are special, which sets them apart from others, and which lives up to their inner ideal while being admired a bit too. Being different & unique is always going to trump being likable or successful (which are mainly sought when they affirm their uniqueness), and a fear of not being able to live their ideals or to fail at their goals can cause them to withdraw.
The 5 wing brings about a tendency for the 4 to doubt their ability to meet the demands of the world. There is the 5 anxiety that they don't have enough energy or the skills to live up to their 4 fantasy ideals. They'll seek to feel more competent by storing up mental/emotional energy in isolation & gaining niche knowledge, and this will certainly magnify how they are different from others, which alienates them but also maintains their 4 ego of being special. They are using double internal markers so to speak - the 4 inner ideal & 5 competency seeking/energy hoarding to craft an inner identity that someday they may actually seek to establish in reality, once they feel equipped enough to do it without sacrificing who they are.