It's rare to see someone get worked up about plywood. Much less a four-star general.

But plywood, yes, those simple sheets of pressed-together timber used to cover floorboards and broken windows, is a particular topic of passion for Gen. Stanley McChrystal, the retired U.S. Army general who served as commander of all U.S. and NATO forces in Afghanistan.

What gives?

"I'll let you in on the secret of plywood," McChrystal said to an audience of about 400 at the 2011 Inc. 500|5000 conference in Washington, D.C. "I lived in a room of it for more than four years. What we did in Afghanistan was we used our spaces to shape our culture."

The "plywood palace," as McChrystal has dubbed the multi-story makeshift office he and others inhabited, was built entirely out of two-by-fours and plywood. And that served their hearts and minds well.

"The beauty is we made this thing when you came in you didn't have to wipe your boots," he said. "When you're in there…you weren't in there thinking 'oh I'm in a nice cushy office, this is great.' You were thinking the guy out in the field had it better."

But his love of plywood runs deeper than dirt on boots. He explained:

Plywood's got a zen-like element to it, at least it does to me. cause when you thinkabout plywood—hopefully you spend a lot of time thinking about plywood—the sheets of plywood are just thin little sort of lousy lumber. You could take your hands and break any one of them. By themselves, they don't have a lot of utility. But when you glue em together suddenly it's stong, it's versitle. If you glue a lot of them together, it's expensive. But if you think about it, compare it to your organization. We build organizations out of normal people. We try to hire the best people, but guess what? We get normal people. Hopes and fears, strengths and weaknesses, problems. By themselves, they're like that piece of plywood; any one of them can break pretty easily. But if they're glued together, then I think they become something special.

To effectively lead a team of real people, you need to press and glue those plywood people together, and make something really strong, McChrystal said.

"And I think leadership is the glue," he said.

"That's why I believe—you can quote this," he said. "Plywood is a state of mind."