How do I know what I know?

I know what I know because that’s what I’ve been taught in school almost every weekday for the last twelve plus years. I know what I know because it’s what my parents have taught me since that glorious day I was born eighteen years ago. I know what I know because that’s what my friends and peers know and that’s what I have learned from them over the years. But is that everything? There are some things that I don’t remember learning from anyone and that I can’t imagine anyone could have taught me. How could have someone been able to teach me how to breath in the first couple seconds of my life fast enough for me to survive? This leads me to believe that some things are just embedded in us when we are born. They are part of our DNA and can’t be untaught. This is that source of the nature vs. nurture debate. I have a deep love for all types of sports, but is this because of my environment and because I grew up in a family that watched sports all the time? At times I feel like even if I had grown up with a secluded tribe somewhere in the Amazon I would have a love for whatever leisure physical activity was practiced and played. A lot of the things I know I have learned from my senses. All of the things I know are based on my trust of their sources, but if I really look deep into it how do I know that what my parents, teachers, and peers know is a fact? How do I know what my eyes and heard are telling me is really how things really look and sound. All that I pick up through my senses is processed through my brain. When you are dreaming your brain simulates these sensations to give you the illusion that your dreams are real. How can I know with one hundred percent certainty that the things that I see and heard aren’t manipulated or originated in my brain? With this in mind the only way I can answer the question of how I know what I know is that I don’t know that I even know what I know.