In the Honeyball Sutta (MN 18), it says, "What one perceives, that one thinks about. What one thinks about, that one mentally proliferates (or complicates)." And this mental proliferation often leads to "evil unwholesome states" which can cause harm and suffering. When we bring mindfulness to the subtle realm of perception, we start to see more clearly without adding anything extra. This is where equanimity comes in, allowing us to meet life with fewer preferences and with greater mental balance.