My idea is that in a very contrasted situation the human eye "does not see the contrast", only the film does. The human vision reacts instantly to different light conditions in the spot it's observing at the moment. So the goal we have, as photographers, if we want to render a picture in a "natural" way, is to flat the contrast (be it done in printing, or after scanning, or whatever) so that the scene appears as our mind reminds it and not as it was for the film.
If the scene is entirely in the shade, it should be exposed normally, for no idea of "shade" (dark) to be given;
If the scene is part in sunlight and part in shade, and using a negative/print process, it should be exposed in a way that allows a sensation of contrast flattening (opening of shadows during printing) that means with most material exposing for the shadows and control highlights during printing;
If the scene is part in sunlight and part in shade, and using slide film for projection, I would preserve highlights from burning and let the rest fall where it may;
If situation as above, but the final product is a slide scan, I would open shadows and reduce global sensation of contrast as in case 2;
If we have a night scene in which there is a great contrast (nocturne scene with lit fountain, monument) when using slides I would expose so as not to burn highlights, and be "glad" that shadows fall into full black as this is a night scene.
If situation as above but using negatives I would aim for the "slide effect" and not try to flatten contrast, letting ample areas of the frame to go pure black if necessary;
If the subject is photographed at night but no "night" is to be seen in the frame I expose to give a "non night" atmosphera;
In this case, and IMO, for a nice and "correct" rendering of the subject on the film all tones must be reconducted inside the film curves "the normal way", without trying to convey the fact that it is a nocturne picture.