Have you ever arrived home after a photo shoot only to find some of your photos came out a little underexposed and darker than what you expected? I am sure you were mindful of the exposure meter and did your best to keep that meter centered but still you are left with photos that are noisy and lacking in shadow detail.
That is when you know that your exposure meter lied and you really should have bumped up the exposure settings to compensate. Over time, experience as a photographer will tell you when it is best to trust the meter and when you should trust instinct.
Foggy and overcast scenes benefit from adding more exposure to get better contrast and shadow detail. If shooting in manual mode, dial in a a notch or two over the balanced exposure mark on the meter or add + .7-1 exposure compensation. Take a few test shots to ensure highlight details are not blown out and adjust until you have detail.
Also keep in mind, scenes with lots of bright highlights and and reflections can trick your camera's sensor into under exposing an image too. Often, a bit of exposure compensation, slightly slower shutter speeds or a tad larger aperture setting with meter reading slightly high will suffice to capture the detail in the low lit areas of a photo.
This will often lead to blown highlights on the reflections or areas with bright light unfortunately. The highlights are expected to be a bit too bright and not a major concern. The brightly lit areas of the scene can be a concern but if shot using RAW format, it is easy to use adjustments like 'recovery' and tonal sliders to compensate. It is also possible to use a bit of the burning tool to recapture some detail in those overexposed areas. The image to the left needed this treament to regain some of the detail around petals, for example.
