Whoever told you that you should “always put your darkest darks next to your lightest lights” should have his (or, maybe, her) teaching certificate revoked. It is true that when you put your darkest darks next to your lightest lights that area will invariably become the focal point of your painting. But, it’s like hitting a mule on the head with a hammer to get its attention: what you get is a cross-eyed mule that staggers. The question: Do you always need to use a hammer? The answer: NO. There are millions of exquisite paintings that do not have a single focal point. Most great paintings have numerous focal points (a place where your eye stops because something interesting happens). Your eye moves through these paintings, stopping momentarily to enjoy subtle contrasts or relationships.

Isolated darks or lights tend to separate from the picture plane interrupting the rhythmical movement of the eye.
In landscape painting these extreme value contrasts destroy the effect of atmosphere. Notice that nature keeps every element in harmony by not allowing extreme value contrasts. Teachers will sometimes say that there are no whites or blacks in nature. This is hyperbole designed to keep students from punching holes in their work. White and black are perfectly allowable when they are eased into surrounding values through the use of gradation.

Sneaking In Your Darks
You can use dark values effectively without them becoming theatrical or obvious by sneaking them in with gradation (a smooth, sequential transition). Instead of placing a value 10 (black) next to a value 1 (white), begin with value 10 and sequentially lighten your values until you arrive at value 1. You have the same contrast, 10 to 1, without the visual “bang” that occurs when these extreme contrasts are jammed together (Remember the mule).