What is this?
Pattern Interrupts are words or actions which interrupt the automatic patterns of speech or action that usually are employed to shut people down or excuse people from thinking.
Why is this important?
Inability or refusal to break unproductive patterns of speech or action will cause you to be ineffective in getting your information or alternatives considered. People develop "communication" patterns in many of life's interactions. An example would be when you walk into a store, a store employee often will ask you "May I help you?" (which is a long-standing pattern) to which you (and most other people) will politely reply "No thank you, I am just looking" almost robotically and without any measurable thought.
While at first glance it appears you are having a meaningful human interaction, careful examination will reveal there is nearly nothing meaningful or interactive going on here at all. The two people are not applying thought or consideration for each other in any significant measure. In fact, if the employee's question is actually used to get the exact response you are likely to give - what does this mean? Could it be the employee does not really want to help you at all?
Pattern Interrupts give you the opportunity to destroy the "appropriateness" of the mindless, unproductive patterns that have been established, and instead force engagement of the other person's mind - their thoughtfulness. When we truly engage one another we become "invested" with others - thinking requires at least some measure of effort and that can put us on track to generate value for each other.
Pattern Interrupts are sort of like giving a robot information quite unlike what it expects - the robot is forced to discover the meaning of the unexpected information - or demonstrate it's inability or unwillingness to do so.