Elliott Ackerman in his book Places and Names: On War, Revolution, and Returning, uses the phrase:
"the crystal meth of purpose".
The book is a group of essays on his trips to Iraq, Turkey, Syria, getting close to the ongoing fighting among Syrian rebels, ISIS, Kurds, Iraq forces, and remembering his days as a Marine in both Iraq and Afghanistan.
His point is that combat with your unit provides a purpose which, at least in his experience, is both addictive and not to be found in civilian life.
I never was in combat. Over my life I've known times where I did have a purpose, one which was at least somewhat addictive. I suspect I'm easily addicted,
