Hey I think the instincts are really hard. Most authors write a paragraph about each, if you're lucky. The three descriptions of each type often aren't insightful. When you go online, you get all sorts of contradictory speculations, and all sorts goofy stuff--eg, "I'm sx first cause I'm SO INTENSE"/"I'm soc last because I hate networking". Etc. I've been kicking mine around for 5-6 years or so and am still open to having someone who knows me and understands the enneagram in depth flip my understanding. However, I've managed to derive a few major principles as to how this works.
- First, your dominant instinct is like...fish in water. Meaning it's your values system, it's what you naturally fixate on, it's where your attention goes...similar to your enneagram type. It can be hard to say, Hey what am I focusing on?--you've really got to think about this in some cases. It can be like with your inferior function in MBTI--a non-dominant instinct stands out so much from your overall perceptional background, you think it's the dominant one. Eg, I thought I was sp-first at first. And I'm...not.
- Your dominant instinct is often a point of minor-suffering-to-outright-batshit-tormented-neurosis. Discomfort. You tend to have self-esteem and ego hung up on this area, and it's often an area of some struggle (similar to your last instinct, except you're obsessed with it). If you find yourself freaking out or drawing the line on something and you're not quite sure where the vehemence is coming from, chances are you're touching on the needs of your dominant instinct. It is a point of insecurity.
- If you've had a lot of pain around your dominant instinct, you can sometimes front your secondary instinct to avoid having the first one hurt. Eg, an enneagram coach once asked me why I wore makeup as a teenager. And the fact was, I mean, I just don't know. I liked it. I didn't think it would make me more attractive...because it was like lipstick on a pig...I was so completely convinced I was undesirable...but I just liked it anyway. But because that felt too intimate and raw and painful to actually articulate to her, I just said, Oh, to rebel from my social peer group. Like a goth, right? Yep, cause I hated them. And she typed me as social-first...which I'm not, but I can't talk about the other stuff.
- Your secondary isn't necessarily a lot of "fun". It's just an area you're perceptive of, without many of the hangups of the first. You can still be awkward or neurotic in it. Eg, I walk into a group and I relate to everyone as the "outcast" because of childhood wounds. I think people hate me. I assume I'm not invited. But, I mean, this stuff doesn't really impact my self-esteem or set me off in any way. I'm more detached from it. I'm not necessarily "good" at the social instinct (eg when people talk about making friends or networking...just NO), but I am still concerned with matters involving groups and humanity...eg, politics, organizations, the Greater Good, diplomacy, etc. I give this area a lot of attention and like to talk about it and know what others are currently up to.
- The last isn't necessarily an area of unimportance, but it's something you cannot be assed to build your life around. Eg, I'm 35 and have no savings, no foundation, I'll never be able to retire, my (temporary) home is in shambles, etc. I don't really care, either. I mean obviously this is a matter of some concern for me and I'm kind of embarrassed to be 35 and this much of a loser, but my self-esteem is unimpacted by my failure to be a functional adult. I just cannot build my life around the acquisition of money, retirement, daily goods, and a stable home life. I just don't value this.
- SX--isn't about the act of sex per se, or "relationships". It isn't about "intensity". It's about sexuality, broadly speaking--including often-unmentioned areas such as desirability, life force, creativity, deep exclusive bonds and/or chemistry with other people, and in a more metaphorical sense, divine union and the Beloved.
SOC--isn't about having friends, hanging out, enjoying groups, networking, etc. It's about the web of interconnection, the bonds between all things, working together to survive, keeping current, and knowing roles (more than hierarchy)--who does what.
SP--I don't really know any misconceptions, but I do think that it involves preserving oneself, not just in the short term, but long term. Sometimes "sacrificing for yourself" or "taking care of yourself" doesn't mean taking long bubble baths and indulging in chocolate cake, but the opposite. Saying no to yourself. Being your own parent. Doing the practical thing for long term survival instead of what you "want" to do.
I hope someone finds that helpful. That's a nutshell recap of what I've learned in my years of study. A lot of this doesn't ever get talked about, but as near as I can tell, it's absolutely true. Good luck.