Some readers talk about paragraphs like they're this magic keyhole into a character's soul, and I think that's partly right, but it's also way too simplistic. A really well-crafted paragraph can absolutely do heavy lifting, but it's rarely just one in isolation. The power comes from the specific, telling detail nestled inside ordinary action. Take the opening of 'Rebecca' – the famous line about Manderley. That's a single paragraph, but it's not just describing a dream; it's drenched in this haunting, passive nostalgia that tells you everything about the narrator's relationship to her own past, her sense of being an outsider even in memory. It's a mood that defines her.
But here's where I push back a bit: a paragraph revealing personality often works because of context, or because it confirms a pattern. If a character stops mid-escape to meticulously straighten a painting on the wall, that one action in a single paragraph screams 'control freak' or 'obsessive,' sure. But if you haven't established the high-stakes situation around it, it might just read as odd. The paragraph has to earn its insight by either contrasting with expectation or crystallizing a hinted-at trait. Sometimes the most revealing ones are the ones where the character tries to explain themselves and their language betrays them – a paragraph of self-justification full of passive voice and qualifiers can tell you more than a page of direct description.
Still, I'm skeptical of the idea that any random paragraph plucked from a book will do it. It's usually the intentionally crafted set-piece moments, or those subtle, almost throwaway bits of business that an author slips in. The real test is if you can read that paragraph and predict, with some accuracy, how that character will react to a different, future dilemma. If you can, then yeah, it did its job.