There’s an analogy that people use sometimes, in cases where it’s hard to draw a line. It involves thinking about grains of sand, and the precise point at which a growing gathering becomes a heap.
Writing about the relationship between the problem of climate change and the impact of individual actions to reduce emissions, Catriona McKinnon discusses the “sorites paradox”—the idea that because removing one grain won’t destroy a heap, removing the next grain won’t either, nor will removing the next or the next.