No, you're not wrong. There are at least two senses in which the term "nadir" is used. There's the nadir of our evolutionary wave, which happened when we completed the descent into matter, and there's the nadir of human incarnation for an individual soul, which occurs on average roughly halfway through the sequence of that soul's human life. Once the soul reaches the human stage, it's no longer guided by a group soul the way animals are; it loses its connection with the spiritual in the world around it, it has to come to terms with material incarnation all by itself, and that typically involves bad choices, messy karma, and a series of increasingly frantic attempts to avoid dealing with the consequences thereof.

When those fail, the soul is left face to face with itself at rock bottom, because only then will it turn to the spiritual resources it has within itself and begin clawing its way slowly back out of the pit it's dug for itself. It's only after that turn has taken place that real spiritual development begins. This also takes place in a smaller way in each life; childhood and youth are spent coming to grips with material incarnation, and generally making a lot of mistakes, which then (once the nadir is reached in that life) become the raw material on which the soul works.