What does 'show, don't tell' actually mean, and is it always right?
It means dramatising something so the reader infers it, rather than stating it — and no, it is not always right. Treated as an absolute rule it produces bloated, exhausting prose.
The distinction. Telling states a conclusion: she was nervous. Showing presents evidence and lets the reader reach it: she checked her phone, put it face down, and picked it up again.
Why showing works. The reader participates, which makes the conclusion feel earned rather than asserted. It is also specific — the detail characterises, where the abstract word does not. "Nervous" is a category; a particular nervous gesture is a person.
Why it is not an absolute rule. This is the part usually left out:
Telling controls pace. Not everything deserves a scene. "They were married for eleven years" covers ground that dramatising would take chapters to reach, and the reader does not want those chapters. Summary is a tool, not a failure.
Telling establishes clarity. If a reader cannot follow what is happening, showing has failed. A brief clarifying statement is not weakness.
Telling manages emphasis. If you dramatise everything equally, nothing stands out. Showing is expensive in words, so it should be spent where it matters.
Some of the best prose tells constantly. Much great writing is direct authorial statement, and a rule that would forbid it is obviously wrong.
The genuinely useful version of the advice: show the things that matter most, and the emotional turns you want the reader to feel; tell the connective material, the passage of time, and anything the reader only needs to know.
Where beginners actually go wrong is not telling as such but telling and then showing the same thing — stating the emotion and then dramatising it, so the reader is given the answer before the evidence. Cutting the statement usually improves the paragraph immediately.
Filtering is the related fault: she saw the door open distances the reader compared with the door opened.
In non-fiction, the equivalent is the concrete example against the abstract claim, and the same balance applies.