For instance, the person in the play has committed a transgression of some sort--such as cheating on a test. The actor is asked to think of something similar that happened to them. If it were me, I would think about how I used to cheat at monopoly. It was kind of fun moving all those hotels around the board on every move so I always won! Actually, you should think of something that has bad consequences.
Back to the main idea. Every time the actor in the play has to deliver her line, she remembers that very private and personal event. And, then she will respond with authenticity—because that is how she would surely act when she thinks about the supposed guilt associated with that so-called transgression.
Now about “raising the bar”.
Once in an acting class, the director told me that I should use the following imaginary circumstance: Concentrate on the idea that my father was in prison in Russia and that the authorities told me he would be dead in 24 hours if I did not write my father’s biography in 23 hours. In that scene I was at a typewriter (old-fashion type—pre computers). And I typed my fool head off. Another actor came up behind me and tapped me on the shoulder and believe it or not—I actually hit him in the face!
Now valence is about the consequences that will occur in the imaginary circumstance if you do not perform as needed. If the director had said to me, “Your dad will die in that jail in one year if you do not write his biography in 364 days” I would have messed around and continued to change the phrasing and corrected my spelling errors—with white out. (Pity the poor fools that do not remember doing that. Look it up in Wikipedia.)
Anyhow, this is what the imaginary circumstance is about. It has to be real to you as an actor. And the valence (the level of the bar) has to be exactly right to get the most authentic and “honest” response from any actor.