There are two basic areas in our brain that combine to make us "human"; the limbic system, which manages our instinctual functions like our emotions, and the neocortex, which is the source of our higher-level thinking and also where we store memories. The limbic system is pretty much operational from birth, supplying us with key skills needed to survive and giving us our emotions. The neocortex, however, is mostly a blank slate when we are born, populated with billions of neurons but with little "coordination" between them.
During our first three years of life - coincidentally the same period we're "attached" (see appendix) - those neurons create connections in the form of synapses as we learn from our surroundings, principally from our primary caregivers, usually our parents. We essentially use our built-in emotions to wire our cognitive abilities to make sense of the world around us. These "definitions of our environment" are the basis of our perception of the present as, later on, we'll continually use this as a "reference system" as our knowledge builds and expands. If all goes well we'll lay solid groundwork for making memories (Self-Esteem) and assessments (Self-Confidence) the two basic operations our neocortex performs. In other words, we learn how to look at the past and plan for the future, the basis for everything we say and do, and also what we don't say and don't do.
A "secure" attachment period will mean that the world we develop in closely resembles the greater world we enter during adolescence, usually via the primary education system. If attachment is insecure, we will need to synchronize what our brain perceives with what it is actually presented. Hopefully, this means we will adapt what we've learned and modify our thinking so that it more accurately depicts reality. If not, then we are likely to develop maladaptive strategies and behaviors (MS/Bs) to reconcile the difference. These differences are at the root of the conflict that we all experience, internally and externally, and are the basis of what we unfortunately refer to as mental illness today.
As adults, the neocortex is supposed to be the manager and controller of the input we receive from the limbic system/emotional center. If, during the attachment process and our adolescence, we don't obtain the full set of regulation skills needed, as adults we'll be left with triggers. Basically, when our lower brain functions perceive that something is amiss, we'll respond in a way - say or do something - that is inappropriate for a given situation. Our neocortex, unwittingly left to explain a gut feeling which it doesn't understand, will usually engage in a cognitive distortion. In other words, we will invent a cause or connection that doesn't really make sense.
The base part of our brain is a driven, selfish machine. It wants to protect us. So when it assesses a concern, it's going to propel us into determined action. And if the neocortex isn't filtering what is bubbling up, the behavior can be downright primitive. This is a key situation to note. If someone is triggered, they may not be aware of what they are doing or saying. In that case the best thing to do is not respond and leave it for another time. If need be, you may need to leave their presence. With more severe triggers a person's logical neocortex mind may not be contributing enough, so anything you say or do can escalate the situation. No matter how fair and calm your words may be, it may be a no-win situation.
To see how this all plays out in adulthood you'll want to look at the Model itself. To better understand some of what is discussed we've compiled an appendix which includes many well-known and agreed-to psychological principles plus some original 4Sight terminology. There's also an alternate Origins diagram which, while a work in progress, is a more complete attempt at displaying how we learn the processes that comprise our consciousness.