Ignorance and the arising of dukkha

Some explanations of the second Noble truth emphasizes the three poisons of ignorance, attachment and aversion as the causes of Dukkha. There are probably many different ways to lay this out, but my question is about ignorance, our misunderstanding of the nature of reality. What is the most basic and important deeply rooted ignorance about reality? What is it – on the most basic level – that we don’t see? What is it about the nature of reality that we are ignorant about? What is it that this bewilderment about reality consists of?