This admonition began as a challenge to an engineering team to think outside the box, to consider the perspective of the "audience" for its product and to evolve a way of meeting the requirements and conditions of that audience without compromising the product.
The more profound our commitment or the deeper our understanding of a subject area or particular concept, the more likely we are to overindulge in the details. A production control engineer describing a maintenance problem may be tempted to give an in-depth analysis of the entire process when a 30-second summary is adequate and appropriate for the audience.
The lesson: In order to communicate successfully, remove detail that is not required to support your purpose and message.
Sometimes our own sense of importance, our egos, our self-esteem, or our concerns about integrity sabotage our ability to simplify a description or response. Asked, for example, what aspects of body language must be considered for effective oral communication, an expert could talk extensively about many psychological and physical influences and effects. However, in most cases, the appropriate response is simple and direct: "The most critical elements of body language are vocal qualities, movement, and eye focus."
The lesson: Less is more. If individuals or groups want or need more detail, trust that they will ask.
Presenters may feel that they are not being thorough if they don't provide all available detail. The difficulty is that the more unnecessary detail you try to communicate, the greater the chance that you will be misinterpreted. You reduce the clarity of what is important. The greater the quantity of information, the more you are giving listeners the power to decide what is significant. That's a risk communicators can't afford to take.
The lesson: Think tactically. Being concise and accurate are powerful forms of risk mitigation.
Early in her career, a seminar participant told us, she had the opportunity to work with a world-class industrial designer. He was an artist and a consummate business leader. She was intensely curious about the process he employed that led to consistently outstanding designs.
"First," he said, "put everything on the table. Think big. Think freely. Don't edit." He paused. "Then start taking things off the table. Be thoughtful about why you are taking them off the table. What will the effect on the whole be? Don't overthink your gut reaction. Learn to let go of your darlings. But when you remove something that compromises the quality, the functionality, or the meaningfulness of the whole, put that one item back."
The "KISS" principle is not about undermining the status and quality of your "product" (effective communication) or about compromises that lead to mediocrity. It is about increasing the end value for the audience through clarity and conciseness, with enough detail to be credible and compelling.
Your audience will love you for that.