The gains in human well-being observed since the industrial revolution are vastly larger than pre-industrial fluctuations in human well-being. No other transitions in recorded history, either positive or negative, are remotely similar in magnitude. When thinking about which future developments might be most important, we should not forget that the size of their likely impact may differ by orders of magnitude. For example, a universal cure for cancer would bring a huge benefit to human well-being, but its expected impact seems likely to be vastly smaller than (for example) the likely impact of AI systems capable of automating most human labor, or the counterfactual benefit of preventing large-scale nuclear war.