Why Live in Fear of Confrontation?

So today my brother came home from playing with his friends crying and when I asked him what was up he told me this.

"So my friend and I decided to start a lemonade stand and we made 36 dollars. But then he gave me 4 dollars and told me that that was for my volunteering."

I already knew that my brother bought a lemonade from the store across the street with his allowance money and spent the entire morning in the sun selling lemonade in our neighborhood. My first reaction was out right anger. I kept grilling him about why he didn't stand up for himself and why he didn't say something to his friend when it was obvious that it was unfair what he did.  But instead, he just hung his head and acted like he was in the wrong. When I told him to go to his friend's house and talk to him about it, he flat our refused and was horrified at the thought of confronting his friend. So I dragged him out of the house and rang our neighbor's doorbell and even then he remained silent and refused to say a single word in his defense. So I spoke diplomatically on his behalf. Ultimately they reconciled and his friend admitted to his unfairness so all went well.

However, it made me aware that my brother was very susceptible to the influence of other people and could be easily pushed around. I take pride in myself for the fact that I believe that I am pretty good at standing up for myself and for what I believe in but some part of me still holds back when it comes to confrontation. I think all of us are like that to some degree. For years, I've been saying that I don't care that my old "friend" and I are at odds because I really have no reason to take notice of her. But I still continue to complain about her persistent haughty and self-aggrandizing nature. If I really didn't care then such things shouldn't bother me right? Right. So obviously I've just avoided confronting her about her loud bragging because I am afraid of confrontation.

Why is it that we all fear it? For my brother, he hates confrontation because he's afraid that he will lose his supposed friends by doing so. For me, I hold back because I dismiss it as beneath me to confront certain issues as an excuse for dealing with it. We're scared at what we might lose or what we might be seen as by being confrontational but in the end if confrontation is carried out in a diplomatic matter, there really is no reason to fear it. So I've resolved to be a little more upfront about my opinions and my feelings. Not so far as to become combative, but just enough to be assertive.