1/640, f11, ISO400
Here is a shot of the Golden Gate bridge that was taken with a significant amount of sky in the image and although it wasn't a particularly bright day the camera metered for the sky leaving the rest of the image looking rather gloomy.
1/400, f9, ISO400
By adjusting the exposure by +1 stop the image is exposed to show the details of the landscape.
1/20, f4.5, ISO400
For this shot into a shop window, the camera has tried to lift the overall light levels of the artificially lit interior which has resulted in an over exposure and at 1/20 sec enough camera shake to prevent a decent enlargement.
1/80, f4.5, ISO400
By stopping down by -1 stop a more representative light level and a more dramatic result was achieved. The mannequins can be seen in better detail, the colours of the dresses are more saturated and the image is appreciably sharper.
1/800, f14, ISO400
The pig artwork is poorly exposed as the camera has tended to meter for the pale building and sky in the background.
1/400, f10, ISO400
Having increased the light settings the details and impact of the subject have been recovered as the colours are much more dominant.
1/80, f5.6, ISO400
Here the light coming through the bright coloured window has dominated the exposure and the chairs in the foreground are lost.
1/50, f5, ISO400
By increasing the exposure compensation by +2/3 of a stop the foreground is now properly exposed whilst the background still retains its light and colourful quality.
1/100, f7, ISO400
In this image of Time Square, the brightness of the sky reflecting from the buildings has made the foreground rather gloomy.
1/80, f5.6, ISO400
In order to recover the colours and detail in the foreground the shot was taken again with +2/3 stop which has lifted the image nicely and balanced the light from street level and from the higher parts of the image.
Although modern cameras have very sophisticated metering capabilities, they have no real idea what it is that you are photographing and can only attempt to balance the levels of light and dark to achieve an average result. When the camera is fooled it is up to the photographer to compensate to achieve the desired result. Nowadays we have the enormous advantage of being able to review a photograph and its histogram immediately to ensure correct exposure. With wet film the only option was to bracket the expected exposure settings to ensure that good result. That bracketing option is still available on good digital cameras and is a smart thing to use for those important photographs when lighting is difficult and the option to examine and retake the shot is not there.