Jamil Zaki: Countless people who sat on the sidelines of this struggle have now joined in. We can ask, as many have, why now? But we might also ask, why not earlier? What kept people — especially those with relative privilege — from supporting previous movements, such as the protests in Ferguson, Mo., following the death of Michael Brown? One key to this comes from research on the perverse relationship between power and empathy. We often think of empathy — people’s ability to share and understand each other’s experiences — as a hard-wired trait, but it’s actually more like a skill. The right experiences, habits and practices can increase our empathic capacity, the same way we can get stronger by going to the gym. There’s a dark side to this idea: Other experiences can cause our empathy to atrophy, like a muscle we don’t use. Power and privilege, in particular, sap our ability to understand others.