A good black and white image, especially a dynamic one, has an evenly balanced amount of black and white to it. This is because of the tonal balance which is necessary in an image, so as to not look unappealing and in some cases, overexposed.
For example, if you are taking a photo of a suspension bridge with a dual perspective, you will need both detail and contrast. The detail aspect pertains to the metal surfaces and the tarmac, while contrast is from the light shining in between the cables and arches etc. Taking this photo in broad daylight, with sufficient white space to make a frame of sorts, for the main subject which is the bridge, will make for a very balanced image. While the side surfaces of the bridge will show up as pitch black, the textures will be visible in the arches, due to the light reflecting off the tarmac and falling on to them.
It is important to note that not all pictures will be as balanced as is ideal. Some subjects such as those shot against a completely or mostly white backdrop will inevitably be more exposed than others. For such photos, you will need to make sure that the subject is sufficiently black, or in case of a person, that their clothing is dark enough to strike a balance.