This question is really where both psychotherapy and psychology begin.
Genes provide the foundation of our personality, and some of the limits.
The rest of who we are comes from what happens to us and what we learn from it. Imagine a one year old child reaching out for something that grabs his interest, as is the habit of a child that age. In any event, she barks anxiously at her child in a voice too loud and strident, then rushes over and whisks him into his high chair for safety. Now assume that this is not a single occasion of mom's bad mood, but a common occurrence, her usual reaction to her son's exploration of his environment. I mustn't take this personally.