Papa Bear, Momma Bear, Baby Bear

Years ago I worked in watercolor for 20 years.  I believe it is the hardest and sometimes most unforgiving medium.  Staining color such as Alizarin Crimson cannot be totally removed even by putting the watercolor paper in a bathtub and scrubbing it.  Because watercolor sometimes has an unforgiving nature, I did more preplanning than I do with oil painting.  Of course, maybe I should do the same with oil.  One of the things I did in pre-planning was to paint a value sketch using Paynes Grey and Pro white on notebook paper.  I was taught that there should be three basic general overall values i.e. dark, midtone and light.  I was also taught they should be of different amounts.  By that I mean if you added up all pieces of dark values, all the pieces of mid tone values and all the pieces of light values they should not be of the same amount.  It is like Papa Bear, Momma Bear and Baby Bear.  I think if they are unequal the painting has more interest.  More interesting I think than a two value painting such as a small white dot on a dark background.  In the painting under the tab Still Life in this website there is a painting titled: A New Day.  In it is a Large Dark (Papa Bear), a small mid-tone (Baby Bear) with light (Momma Bear).  Also in the painting under the tab Private Collection is a painting Titled: In a Mirror Dimly.  In this painting the Papa Bear is the dark, the Momma Bear is the mid-tone and the Baby Bear is the light.  Like someone said all rules are there to be broken but the Bears are a thought.