My go to example for "show don't tell" is Les Miserables. The novel is routinely criticized for spending inordinate amounts of time describing things with excessive detail, such as 14 chapters to open up the book describing the bishop to establish that he, in fact, was a good man, had endlessly given to the community, and only withheld two silver candlesticks and a set of silverware as personal comforts. This does give context to the forgiveness of Valjean, but 14 chapters worth?
In contrast, the musical has three scenes in one song with the bishop; one where he welcomes in Valjean after everyone else has mistreated him, one where Valjean is reflecting on the bishop's generosity and how he suspected his motive before stealing the silver, and then one where the bishops not only forgave Valjean, but gave him the candlesticks as well, informing him that the bishop, "bought his soul for God", which drives the rest of the action of the musical. All these scenes only take 3:26, but they are so effective because they show the kindness and mercy of the bishop as it relates to the protagonist, rather than explain at length that he is kind, as well as cuts out details which are irrelevant to the plot.
And yes, there definitely are times where telling is appropriate and useful. But, I like how one of my writing teachers at university put it: rules are there to be broken, but only after they have been used extensively so you know the strengths and limitations of the rules.