The awesome totality of the combined, accumulated, piled up and towering knowledge of the human race has established that we can say with great certainty that we cannot be sure about very much.
We have learned, for example, that so immense is the Universe that for every grain of sand on our planet there are about 10,000 stars.
Once you start thinking in those numbers it's pretty hard to be certain you know a fraction of anything.
Pretty much everything is unknown and truly this is a liberating thought for your personal ambition. Moving into the unknown ...