I propose the following:

Imprinted parents and baseline emotions

In the first 6-8 months of life, babies permanently imprint the faces of people they look at a lot. Imprinting is a biological process, similar to what happens in baby animals like geese. I refer to people whose faces are imprinted in the child as imprinted parents. 

Interactions with imprinted parents are special. Fear and some other emotions (which I'll describe in detail in other sections) evoked in the child during interactions with imprinted parents become permanent (i.e. constantly active) and overly sensitized (i.e. easily triggered).

For example, children who are punished by an imprinted parent experience fear. As a result, those children feel some level of fear all the time. Additionally, their fear responses become overly sensitized - they are likely to over-interpret their environment as threatening and react with a fear response that is out of proportion to any actual threat.

I refer to emotions acquired from interactions with imprinted parents as baseline emotion - permanent, sensitized emotions that remain active throughout adult life.

While most childhood experiences evoke emotions, only interactions with imprinted parents produce permanent, baseline emotions.

Humans have widely varying mixes of baseline emotions due to their wide range of childhood experiences with their imprinted parents. 

Baseline emotions are mostly perceived as normal. People have very little awareness of their baseline emotions, although they may be aware of some of their effects, such as discomfort in social situations, depressed mood, or being overly talkative.

Baseline emotions do not significantly change during adulthood.

Beliefs

Children remember their experiences, especially ones that evoke significant emotion. Their brain synthesizes these experiences into a world view. I call this world view their beliefs.

Putting it together

These two factors, baseline emotions and beliefs, determine almost every important personality trait.