The event horizon is the technostist term for the moment at which automation becomes cheaper than traditional human workers for any specific task. The term is a reference to the technological singularity.
The idea behind the event horizon is that automation becomes cheaper, in part due to automation itself expanding the economy. As the price of materials, programming, and usage falls, machines become an alternative to the use of human workers. Other external factors include rapidly rising wages— a high minimum wage incentivizes business owners to rely on automation.
There comes a point when robotics become cheaper than human workers in all fields; the cost of STEM-trained human programmers exceeds artificial neural network programmers; the mining of raw materials becomes automated; and machine workers learn new tasks faster than potential human workers. The price of automation collapses to near zero, and the event horizon has been reached. Beyond this point, human workers become a liability as compared to machines.