I think the tell and show problem happens because in the throes of creation we're grasping for main points of action and reaction and variations of them. We want to get them down before we lose them. I do this. A lot.
So what happens is we get the structure of a paragraph wrong for fiction. Our paragraphs, in an inexperienced writer this can be many, many paragraphs, become structured like we learned to structure them in our high school essays. Topic Sentence. Development of that topic sentence. Repeat and repeat and repeat.
We tell the reader what we're about to show them and then we show them.
And we don't see it because we tell ourselves we are showing. But the problem is we're telling first and then we're trying to show with the rest of the paragraph. Causes lots of problems. For example, it drains a paragraph of suspense. If you tell the reader what will happen first and then show it, well they know, don't they. It makes the paragraph feel repetitive and sometimes clunky. Often it will even undermine development of the paragraph because the author won't see choices he would if he were in the mind of his character moving forward. Above all, it weakens the verisimilitude of the paragraph.
Instead of telling and then showing--just show. We want our paragraphs to stay in the POV of the character experiencing the scene. We want to experience it with them. See it through them.
Like I said. I still tell and show. But in revision I'm conscious of this problem and I look for it and do my best to stay in POV. I think it's made my fiction stronger. Hope this helps.