Basically, Shawshank clearly establishes itself as having a gritty, realistic tone, where shit happens for reasons that have no cosmic significance or relation to your epic hero arc. Specifically, when that prisoner turns out to be a witness who can clear Andy, and just suddenly gets shot by avaricious guards who don't care about the injustice. (If it hadn't been already, Red's final parole speech cements that tone.)
It's a huge betrayal of that when you turn around and say "oh man, if you just belieeeeeeeve in yourself hard enough you can somehow make a figurine carving tool last 100x longer than is realistically possible and accomplish major excavation work, it's all about your force of will".
(Similar complaint about Interstellar, which commits to hard sci-fi enough to include an expensive, photo-realistic black hole, and doubles back and resolve the plot with "ah man we just have to tap into the mysterious fifth-dimensional power of love!")
For example, suppose a character sends a spy to accomplish an objective. Meanwhile, another group of people are also trying to do this, which will benefit the main character, although the main character is unaware of this. The second group gets there first, and even though there was considerable buildup to the spy's mission, in the end, his presence doesn't matter (much).
If you want as lean a story as possible, you would cut out the spy's mission altogether, but its presence gives a sense of realism, because the character in the story doesn't know ahead of time that sending the spy would be redundant.
On the other hand, building up readers' expectations with details that turn out to be irrelevant is just deception. See the last season of Game of Thrones, for instance. All those characters that were carefully built over the last seasons get discarded without any explanation.
There's sometimes stuff like that in Tarantino movie, like the outlaw lady in Django.