Let's illustrate this with a graph. Let's call it the Laugher Curve, and borrow the inverted U from the much loved Laffer curve. But here, the Y axis is The Value of Human Life, and and the X axis is The Value of Technology.
To the left of the curve's peak, as the value of technology rises along X, the value of humans also rises along Y. Clearly technology is augmenting human labor and increasing the value of human workers.
Further to the right the Laugher Peak is approached, and the rise in human value slows because for some jobs, augmentation has turned to automation. Machines begin to automate more tasks more than they augment. Ergo, when the number of automated tasks rises sufficiently, machine replaces man.
Then as displaced humans seek new jobs, they find themselves taking positions of lesser value because they lack the skills or ability needed to qualify for those remaining jobs of equal value due to those jobs' increasing complexity, which was caused by their rising tech augmentation. What many humans do best, now a machine can do cheaper, and the retraining of those humans for equally valuable jobs has become unprofitable.
Further to the right, human augmentation by tech fades and automation is in full swing -- replacing those humans with marginally greater and lesser skills. Finally when we reach the right edge of the curve, all humans have been made redundant by tech; they're unemployed. At last, the net present value of mankind falls to zero.
[It's called the Laugher Curve because it's believed the original Laffer Curve was never about taxes. It was just a pretext to encourage those folks who valued tech more than people. It also cleverly refers to the oxymoronic outcome of a temporal mobius loop, in which the final laugh was on those who could laugh, by those who couldn't.]