There is nothing so practical as a good theory.
Picture yourself moving very slowly in stop-and-go traffic on an expressway. You're listening to the radio and thinking through the agenda for an upcoming meeting. You've come to a stop and are looking ahead at the lanes of stopped traffic ahead of you.
Wham! Another vehicle has slammed into you from behind. You jerk forward against your seatbelt. Coffee sears you and coats your console. Your back seizes.
You get out of your car and survey the damage. The rear end of your car is badly contorted. Your back hurts. You feel frustrated, angry, and anxious about all the tasks that now lie ahead for you.
After logging a claim with your insurance company, you consult a famous plaintiff's counsel for advice. After listening to your recitation of the facts, counsel says that to proceed with a lawsuit, you have to have a legal theory that applies to the situation. She explains that a theory is a statement of the legal principles tested in litigation and formalized through appeals over hundreds of years in our and other legal systems that describe both (a) a pattern of behavior and (b) the legal outcome resulting from that behavior.
Counsel quickly summarizes the facts in your case: It was a sunny day, early in the morning, with stop-and-go traffic. You were stopped and were hit from behind. Counsel then advises that the relevant legal theory is ...