The event horizon is a term used to describe the threshold of a Black Hole, beyond which gravity becomes so strong that not even light can escape. The event horizon defines the black hole's limits, where the escape velocity is equal to the speed of light.
But it is not clearly marked. Physicists think of it as imperceptible. A hypothetical astronaut entering a Black Hole would not know (s)he had passed it.
The event horizon is also a time horizon. Neither time nor light can escape once trapped in the black hole. (Steven Hawking, a brief history of time). But for human planning purposes, a time horizon marks the limits of current planning. It is assumed to be a fixed point of time in the future at which point certain processes will be assumed to end, or at least need to be reevaluated. An agreed-upon time horizon is necessary for finance, accounting, and risk management, in order to be able to compare different alternatives in a consistent manner.
In The Ministry of the Future, Kim Stanley Robinson describes the tragedy of the time horizon. Because we can’t imagine the sufferings of future populations, we do little about them. “But by the time they get here, those problems will have become too big to solve” (p.172). Robinson links this tragedy to the economics of the discount rate, which considers costs in the present to far outweigh costs in the future. And like the event horizon, there is nothing to mark points of no return.
In this example, along with the notorious “Tragedy of the Commons”, some structural feature is considered an inevitable consequence of human nature – in both cases a drive towards narrowly conceived and short-term self-interest over any shared (and long term) public good. While Capitalist markets are claimed to align personal interest with the common interest, examples of “market failures”are held up as requiring correction by laws and the state’s enforcement. Their costs (and benefits!) are discounted by Capitalism. (see The Tragedy of the Commons)