Youthful optimism can be hard to find in Japan, where millennials rank as the gloomiest of those in the world's biggest economies.

While a majority of young adults in its trading partners see bright futures and successful careers ahead, fewer than 40 percent of Japanese do, making them the most pessimistic in 18 countries surveyed by ManpowerGroup. They're even more downbeat than young Greeks, who have suffered Great Depression-like conditions and political upheaval in recent years.

So much for efforts to eradicate Japan's "deflationary mindset." As Prime Minister Shinzo Abe tries to engineer an economic revival, young Japanese are far from bullish. It's weighing on the economy already and poses challenges for the future.