Continuity Exists So You Never Have To Think About It
The rules of screen direction and eyeline are not aesthetics. They are a maintenance system for the audience's mental map.
When two people talk, an audience quietly constructs a map: he is on the left, she is on the right, the door is behind her. That map is fragile and enormously useful, because once it exists the audience stops spending effort on geography and can spend it on the scene. Continuity conventions exist to protect the map. Keeping the camera on one side of the line between two performers means their eyelines stay opposed and the map holds. Crossing that line without preparation swaps them, and for a second or two the viewer is doing spatial admin instead of listening. The rule is not sacred, but breaking it always costs attention, and the cost should buy something.
The same logic governs screen direction in movement. If a character exits the right of frame and enters the next shot from the left, they read as continuing the same journey. Reverse it and they read as turning back. Audiences apply this rule without being taught it, which is why chase sequences that ignore direction feel incoherent even to viewers with no technical vocabulary. They are not confused about the plot. They are confused about where everybody is, and that confusion registers as boredom, because a viewer who cannot picture the space cannot invest in the outcome.
Deliberate breaches are a legitimate tool. Crossing the line at the moment a relationship inverts, or cutting to a reversed eyeline as a character's understanding of a situation collapses, uses the audience's disorientation as content rather than as an accident. The distinction between a technique and a mistake is entirely a matter of whether the disorientation is doing a job. This is the pattern across every craft discussed here: the conventions are not moral rules, they are descriptions of how audiences process images, and they can be broken by anyone who has first understood exactly what the breach will cost.