I found this part to be most accurate from Pink, "Brooding means to dwell on a subject or to meditate with morbid persistence," but not a whole answer to question posed in this thread. I definitely think there is more to it.
Welcome, Heather, and kudos to you for jumping right in.
Being an Enneagram 1 (reformer) and (with the trait highest of perfectionism at 75%) I struggle with moral correctness in private or living life right so as not to be found in the wrong and needing clarity of what that entails. Perfectionism is a continual struggle and may be also heavily blurred with some idealism.The greater the disparity of the ideal and the real the harder to integrate the disappointment for me.
I struggled SO hard with perfectionism (still do). When I was in 4th grade and got ONE B on a card full of As, I burst into tears, went to my teacher, and said, "Why didn't you tell me?! I could have DONE something about this! WHY?!" Thank goodness he was an INFJ and was able to settle me down (while looking disturbed).
Not to say that I always made As. Just that when I was pulling them down, I wouldn't settle for less. In elementary school, I was in gifted classes with my sister, and it was something of an internal competition amongst my friends for annual test grades. I have no idea WHO thought that was a good idea -- to place so much pressure on children of that age who aren't mature enough or experienced enough to handle it. I mean it was architectural studies with detailed reports on historic homes we toured and specific designers (with designs of your own made in 3D), it was running your own business and making it work, it was global culture and a huge cohesive presentation made about it. I wasn't even out of 3rd grade and already I had this super competitive streak that was, in my opinion, consuming.
Years on a swim team was an outlet for the same thing - exerting myself and getting the best of someone else. 2nd place was almost NEVER enough and it could ruin my day. There was one girl in particular from another team from the posh end of the city that I was perfectly matched against, but I liked her, so competing against her was sharpening not aggressive. We looked forward every year to standing at the blocks and chatting and then putting the pedal down on each other. Some years she won, some years I did. It was great for my conquering nature to be cowed at times, then rewarded by a worthy foe.
I see a very strong tie between competition and perfectionism. Perhaps I'm off base?
I don't know what Enneagram type I am.
In private I dwell or brood and it easily magnifies the problem (or in reality what is a small irritation) and I lack objective perspective (the Ti maybe). Righteous anger at violating a value (in myself or received from another person) also works me up. Generally negativity is hard to push aside and the internal dialogue is not always positive at all. I have made a choice to downplay ulterior motives (that I perceive esp in women/manipulative ppl) and take things at face value in conflict to help alleviate some of this.
I can relate. Righteous anger is the bane of my existence. Someone once told me that I reminded them of Nemesis. I thought it was strange to say at the time, but I looked into her and saw that it resonated deeply with me. She wasn't a violent woman, she was obsessed with righting wrongs, esp for those who couldn't fight their own battles. It was less revenge and more avenging.
I used to dig at the real meaning of a person's words (esp when my BS meter detected a lie) and I found it exhausting (because liars are exhausting, like chasing a rabbit through a warren of tunnels) until I decided that even if I *could* see a lie or a half-truth, I was going to let it ride and watch how it unravels. Choosing not to care *that much* was a relief to me.
The highlighted part, were you manipulated or subjected to unjust restrictions/punishments growing up?
Maybe also it is "fun" to be identity seeking in private and searching for who I am that may be hidden from even myself at times. This doesn't always lead to cheerfulness and I need some light fun or personal extroversion to pull me back up from the depths that I am coming up blank on.
I frequently frustrate and surprise myself with elements about myself that I didn't know were there. My ENFP sister has learned to take a lot of what I do in stride, because who knows what's going on under the surface? Sometimes even I don't, though I spend a great deal of my time brooding and trying to dig at myself to get to what I know must surely be the key.