It's easy to think people are stupid, ignorant, arrogant, selfish, insensitive etc.
It's much harder to come to terms with the fact that they are what they are because of everything they've been through, that they have had a lifetime of experiences that very likely don't mimic our own.
We think their behavior doesn't make sense because they are outliers to our mental models of the world we've experienced.
We don't realize that within their mental models, their behavior makes complete sense.
We don't all live in the same world. We live in projections of our own mental models, which are as wide and varied as they come.
All behavior makes sense, given enough information.