But there is something we can and must do: We must learn all the lessons we can.
Here are some:
1. The gulf between the decent and the indecent
Tamerlan Tsarnaev, the older brother, once told an interviewer before a Golden Gloves boxing competition: "I don't have a single American friend. I don't understand them."
The reason Tsarnaev didn't understand Americans was not primarily cultural. Tsarnaev came to America when he was 14 or 15, an age when the vast majority of immigrants to America have assimilated quite successfully
Rather, the reason was that the indecent don't understand the decent, just as the decent don't understand the indecent.
One of the greatest insights I learned as a young man came from reading Viktor Frankl's seminal work, "Man's Search for Meaning." Frankl was a Jewish psychoanalyst who survived Auschwitz, where nearly every member of his family, including his wife, was murdered. His conclusion: "There are two races of men in this world but only these two. The race of the decent man and the race of the indecent man."
Those "races" do not understand one another. But more important than understanding the indecent is overpowering and, when necessary, destroying the indecent.
2. Any religion or ideology that is above good and evil produces enormous evil.
For tens of millions of Muslims today, Islam is beyond good and evil: The infidel may be decent, but that is of no importance to the radical Islamist. For example, to become a "more religious" Muslim, Tamerlan Tsarnaev gave up boxing, marijuana, tobacco and even not wearing a shirt in the presence of females. Tsarnaev believed Islam forbade those things -- none of which is an evil. But when it came to the greatest evil -- murder (of non-Muslims) -- his religion was not only silent, it was enthusiastically supportive.
Likewise, communists in the Soviet Union, China and elsewhere -- and their many supporters in the West -- raised the creation of egalitarian society and industrialization above good and evil. And Nazism elevated race above good and evil. The environmentalists who oppose vitamin A-injected rice in the Third World place their agenda above good and evil.
Unfortunately, most religious and secular ideologues find preoccupation with human decency boring. The greatest moral idea in history, ethical monotheism, doesn't excite most people.
3. A victimhood identity produces cruelty.
Dennis Prager is a SRN radio show host, contributing columnist for Townhall.com and author of his newest book, “The Ten Commandments: Still the Best Moral Code.”