Why can't grownups see snakes?

I had this dream when I was little - about five years old. I still remember it vividly. I was on the steps of the school I attended and two giant green cobras were coming up the walk, I was doomed. There were only two steps up the the brick orange double steel doors that allowed entry into the main hallway. Each door had three square windows about a foot wide down the center in a vertical line. Inside, the pine paneling lined hallway looked cool, dim and safe atop the dark green tiles.
But I couldn't get up the steps. I needed help. There was nobody around. I looked down the walk and the snakes were getting closer and closer, their shiny greenish brown eyes looking right at me. A teacher came to the door from inside. She had short, dark hair and wore a pale dress with a white belt. She peeked her head out the door and said I didn't need help - that I should just come in. But I couldn't. She didn't believe me - that I needed help when I asked for it or that I knew my own limitations and capabilities - never mind that she was blind to the sharp and gaining danger that was really there had she bothered to look. Grown-ups never trust kids to understand what they can't. I was so scared. I was only five for God's sake and there were poisonous snakes about to kill me. Who wouldn't be petrified with fear? That was the end of the dream. I woke up. Glad to be in my dark room, but still alone.