What is the one most astonishingly dumb things that, as a child, you believed was absolute truth?

I thought that all languages were actually the same, just our ears differed. So e.g. as a native German speaker, I thought all people 'speak' German (I.e. make the sounds of the German language), but the translation of sounds into thoughts by the ears would only work when the source was 'my version' of the language. Very hard to put that into words, I just realize...

Another thing was that I had my own religious philosophy. I believed in reincarnation, and thought that all life was just a giant circle where you would be reborn as your own worst victim. Only when you have lived a victimless life, you would ascend into heaven. My go-to example back then was if you stepped onto a worm you will be reborn as a worm that is being stepped on. This one has horrible victim blaming implications when you think about it but in my childlike naivety I thought it was very fair.