We see impossible things just fine.
It's not that our mind can't see them, it's just that we can't comprehend them - we have no idea what it is we're seeing because we have no idea how we should be putting those images to ideas.
When the Native Americans saw the ships Columbus was in, they would first have seen the sails, and been confused by what was going on. When they saw that they were boats, they would have understood - "these are big boats, like the ones we use to sail around the island." Remember, Columbus landed on the island of Hispaniola.
At any rate, whoever told you that the Indians on Hispaniola couldn't see the boats was wrong.