见微知著

one tiny clue reveals the general trend (idiom); small beginnings show how things will develop

to examine tiny clues to know general trends (idiom); to deduce the whole story from small traces

lit. see a tiny bit and understand everything (idiom)

lit. the falling of one leaf heralds the coming of autumn (idiom); fig. a small sign can indicate a great trend

lit. seeing clearly the downy feathers of autumn (idiom, from Mencius); fig. perceptive of even the finest detail

to infer easily; to guess at a glance; to get a clue