There is no more difficult art to acquire than the art of observation.
A good actor will tell you that one of the most important activities on the stage is listening. Parallel to that is observing. It is important to pay careful attention to everything that is going on in order to be completely involved in the character and the play. There are exercises and tests in the various arts to improve one's ability to observe.
When I was learning how to draw, my teacher would sometimes work us to distraction with his fiendish observation exercise. He would have the model take a pose and hold it for one minute, then relax, and we had to draw the pose from memory. I finally began to do it by observing, not the details of the arm, but in what direction the arm was going. From shoulder to elbow it is pointing to the edge of the model stand, the forearm is pointing toward the window and if the fingers are spread out, each one has a specific part of the room they are pointing to. It sounds dreadfully complicated but it isn't if you develop a good sense of observation.
Observation comes in two similar forms, or results. One is description and the other is reconstruction. In a classroom of acting students there are exercises for both.
The student looks at a photograph or a painting for one minute. Then the picture is removed and the student has to describe it: the subjects, where they are placed, the dimensions of each compared to the others and the colors employed. I thought I was fairly good at observing things until the first few times I tried this test.
Reconstruction exercises can be even more difficult. The student looks at a table top with a bunch of objects on it, Then the actor turns his back and the objects are rearranged or removed. The actor turns around and has to put the objects back in their original positions. This exercise is also done by having other actors sitting in a row, in various poses. After a minute the student turns his back. The actors then rearrange themselves and change their poses. Then the student has to put them back the way they were. If the actor has his feet crossed it isn't enough to say "cross your feet." If he originally had the left one over the right one and then changed them, that's something the student has to notice.
A good, well trained actor can walk into a restaurant, take a seat and tell you, if you ask him, how many tables are behind him, how many people are sitting at them and where they are.
I was doing a show in Virginia and on the day of the technical rehearsal, which comes the day before dress rehearsal, which comes the day before opening night. the scenery was finally in place. It was a complicated set with doors and stairs. I walked all over that set looking at everything. Some people thought I was crazy and wasting my time. At another theatre in Virginia I was in a show with a complicate set and the director asked us to walk all over it and set aside rehearsal time for us to do it. In both cases I had a firm knowledge of the environment of that play.
What if you were suddenly called upon as an eye witness of an event? How well could you describe it?