Understanding (in a car crash)

There are so many things that make us up. Some things we control, some we control or affect without realizing it. Some things we have no clue affect us the way they do or even THAT they do.

...what we call personality is to a considerable degree a question of brain chemistry. There are a score of different ways in which this one chemical, serotonin, can be related to innate differences in personality. These are overlaid on the score of different ways that the mind's serotonin system responds to outside influences such as social signals...social behaviour is not some external series of events that takes our minds and bodies by surprise. It is an intimate part of our make up, and our genes are programmed not only to produce social behaviour, but to respond to it as well.
Genome. pg 172 by Matt Ridley

Just another thing to think about in terms of understanding. There is so much that goes into who we really are. But the degree to which things do affect us, well that can't be so easily stated.