Even when saying nothing, one’s “four limbs”—that is, one’s posture, facial expressions, and so on—can express one’s attitude.
In short, experiencing some sort of discomfort or lack of attention can lead to, if not an inappropriate action, then perhaps a facial expression or other “microaggression” that helped to generate another person’s problematic response. Confucians well understand the ways in which our dress and body language can encourage others—often subconsciously—to respond in positive or less positive ways, which is one of the reasons for their emphasis on ritual. Such a reaction then forms part of the “situation” to which the other is reacting, and so (partially) explains their reaction, rather than it simply being a result of under-developed character. It is crucial to note that the way in which one is contributing to the situation (via “microaggression”) is usually not intended or even conscious. Mengzi is suggesting that if we look carefully at our own motives, we may discover underlying factors that are affecting the outcome.