One of my posters wrote that perhaps this German pilot suffered from accidie, which is generally considered mental sloth. It's more than that. It's ennui, boredom, meaningless, hopelessness, not being connected to anything. I read years ago that some people committed suicide out of boredom. That's accidie.
I use the example of insomnia. When you can't fall asleep, can't think of anything to do, you are bored and things seem meaningless...that's the beginnings of accidie (Stephen King once wrote one of his typically enormous novels about a man suffering from insomnia. It was of course called Insommnia.)
This suicidal pilot, to me, appeared to be envious ("If I can't be happy no one can, so I'll take 150 innocent people with me"). But perhaps he also considered life meaningless, so he decided to go out in a blaze of glory. Hubris and accidie? Perhaps. It's not as if you can suffer from just one.
I use the Seven Deadly Vices and Seven Cardinal Virtues to explain people. They have been around for thousands of years, and came from the Greeks and were adopted and expanded by Christianity. They're not "religious." It's more like practical, useful psychology that can be applied to everyone.
'Accidie has always been considered a sin, although, as I have written many times, "sin" means to "miss the mark."
When you suffer from accidie and hubris people don't seem real anymore. They're just props in your personal play. Instead it's all about you, and it doesn't matter if people live or die. Or if the suffered lives or dies, either.