"A Course in Miracles" starts at the level of stating basic principles, but customary thinking in the world generally operates at the level of specifics. The Course refers to the specific, or concrete, level as being the level of the ego belief system.
A brief working definition of 'principal' is, "An abstract statement of a basic truth or law."
Since many people come to the Course with a head full of specific ideas about what miracles are, or look like, one of the biggest challenges beginning ACIM students face is the task of reconciling the very concrete ideas they may have about miracles with the consistently abstract level of discourse offered by the Course.
However, this does not minimize the significance of specifics when working toward the over-arching change of mind that is sometimes known as "awakening."
The Course tells us that correction must be introduced from the bottom up and, as far as I can tell, this means starting with specifics. Heal just one specific broken relationship today. Don't worry so much about the big picture, which is beyond our grasp anyway. Take just one small step in the direction of God, for as it has been said before, it is better to light one small candle then it is to curse the darkness.