This hit like a ton of bricks. There are days when I could easily identify with these Japanese men. On the days where I'm more outgoing, confident, and social, I've noticed that feeling productive -- and what I deem to be "happiness" -- go hand-in-hand. It could be something as simple as helping a friend set up their wireless router or tutoring my niece in math. It's almost as if I allow myself to be a part of society once I feel like I've earned it -- as silly as this may sound to those who haven't experienced this phenomenon. Ultimately, and I'm not saying it's a panacea, but what never fails for me is to attain some feeling of productivity or importance.
When I was a kid, my dad told me something that has always stuck with me: "Pretend like everyone you meet has the following sentence stamped on their forehead: 'I want to feel important'".