If I told you that cheese gives you nightmares, you would probably laugh in my face at first. But if I told you about how one night I ate a bunch of cheese and then had the worst, most terrifying nightmares of my life, you might listen to me. Some of you might take what I say to heart and believe it right away. Others might at least go to the internet and do some research of your own. The point is, you would listen to me.
When an 8-year-old makes the same claim and tells the same story, you pay no mind; it's just a silly child.
Why do you make this difference? Why do you trust some over others? Our claims are the same, as are they based on the same experiences, but mine warrant some respect, while a child's does not.
As I wrote this, I realized that this is how ethos really works. And even if you one who says that a person's degrees titles don't impress you or affect your thoughts, you are still being affected by people's authority. Sometimes it is just the authority of a person having lived more years than another.