I met him one night at a dining facility, or DFAC, at a base in Kabul in 2009. He was young, energetic, sharp, and eager to fight terrorists and the Taliban. The officer was impressive. Two days later, he was seriously wounded in a suicide bombing and medevacked out of the country.

I met him again, quite by chance, four years later back in the States. I recognized him immediately. I introduced myself, acknowledging he probably would not remember me, given what had happened to him shortly after we had met. In oddly slow, carefully formed words, he admitted that he didn’t recognize me. He told me about the shell fragments doctors had extracted from his skull. He didn’t say that he had brain damage, but I assumed as much.

For many people like myself, that was the war zone experience. You...