Can someone clarify the "Show don't tell" thing?

In all fairness I don't like the show don't tell rule. It's too much of an absolute, but I guess they say that for beginning writers. In my years of studying writing, I've learned that show don't tell should be something like Show and Tell, but Tell Much Less. Sometimes in a book or short fiction piece, telling is necessary because the thing being told is not so important that the author needs to spend pages showing, but it is just important enough that it needs to be told. It's complicated and only the more experienced of writers can pull it off.

"It was the best of times. It was the worst of times." Such a big tell, but it's the beginning of a highly revered novel.

Show don't tell is a general rule of thumb but by no means does that mean it can't be broken. When you find instances where telling works, you should make note of how the author did it for your future reference.

Edit: Visit the link below and scroll down to the Sometime Telling is Good Section. I like how this blogger explains it.

It is show, don't tell most of the time, but there are times to tell, don't show. For instance, if your scene is done, and the characters finish off their day before the next major event, you don't really want to write, in great detail, what they ate for dinner and how they slept. It's enough to say something like, "It took three long days to wait for the test results, before..." then the entire rundown of the people waiting for the test results.

Also, you have to remember fiction has become refined over the years. Publishers got downright picky in the last few decades, so much of what you've read was from previous ages. In today's standards, the classics would never be published. Even "Moby ****" has some serious flaws readers sense, but don't understand. Very few people read the chapters devoted to whales and whale hunting - it's just too boring, and yet, it's still an all time classic.

I can't remember every place I've ever read how to know when to do either, but below is a link to one book that I know will help you with this question and many more. It's a classic too, but keeps getting updated, because of the changes in the industry.