Suppose you were born 5000 years ago. You wouldn't be born into nothing, but into an existing culture. You'd learn a language, behaviours and ways of thinking about the world. This would be your world with all its possibilities, but also all of its limitations.
Even if you'd be really smart, you couldn't have invented any tool, idea or technology we're using today. We're not any smarter than our ancestors, but humanity's cumulative knowledge gives us tools and inventions any of our ancestors could only have dreamt of. Any normal person of today's age fluent at reading or in calculus could have easily outperformed you.
We're bound to the context we live in. We're bound to the borders of our world. What's so interesting about this thought is that you don't need a massive brain, but you only need to be able to see and connect ideas.