The big thing to realize is that metering is an art to be learned, and which is the purpose of the compensation functions. Beginners never want to hear that, they want to imagine the camera is supposed to always get it right. It doesn't of course, but they will persist with that for a while, but then hopefully, most will eventually try to learn how reflected meters actually work.
The meter is an excellent guide, certainly almost ballpark, but often our head is our best tool about using it.
So we tend to suppose that the camera meter exposes the portrait face this way, and the background that way, etc. But it doesn't. There is only one exposure for the entire frame, and the light meter is too dumb, with no clue what any of that stuff is, or how it should be. The meter cannot tell the difference in a black subject with much light on it, or a white subject with little light on it. It just sees some light, which it can measure, but then what? It has no clue what it is, or how it should be. In every case, the only possible metering goal is that the average of the scene should be about middle gray (a compromise for safety, not too dark, not too bright). And the simplest experiments always show that is very true.
But which does in fact work pretty well, at least for very many "average" scenes, scenes which do contain a wide mix of bright and dark areas and colors, some areas brighter, some areas darker, and the average is often in fact in the middle, so it often magically works. But there are many exceptions too, which is what compensation is for. It is not that hard, we just learn that when we walk up to a white background wall, or a dark open area behind our subject, the alarms will go off in our head, and we know we will need to tend to the compensation. Or at least digital shows us the result, and we usually have another chance. I suppose one difference in beginner and advanced, is that advanced expects this, and gives it proper attention.
Light meters were inexpensive and popular and built into cameras 50 years ago, and every photographer ever using them has needed to know this. So learning how the meter works really is about the biggest of the big deals.