When you are using your camera’s auto mode setting, the camera is making all of the exposure decisions for you. It’s “gathering data” from the scene, adjusting the exposure settings and then goes to work to produce the best possible image, given the conditions. Sometimes, however, the camera is not able to render what you think is an accurate depiction of the scene.
For example, harsh sun, low light, shadows and other light extremes may present too many variables for the camera to handle. This may require the use of flash, changing your shooting position, or switching to the Manual Mode and adjusting the exposure more to your liking. Even then, in extreme cases there will be times, unfortunately, when “the shot” will not work out and you’ll need to optimistically carry on.