Finland is home to the world's happiest people. Their No. 1 secret is this 500-year-old mindset, says psychology expert

“Sisu” is a concept and way of living that has been interwoven into Finnish culture for more than 500 years .

It has no direct translation, but it is focused on determination and fortitude. It’s about having the grit to push forward in the face of adversity and near-impossible odds.

For six years in a row, Finland has ranked No. 1 as the happiest country in the world .

According to research from psychologist Angela Duckworth , we can endure so much more when we work towards something that contributes to the world beyond ourselves.

To gather firsthand data on sisu for my PhD studies, I completed a 1,500-mile running expedition across New Zealand. I dedicated my run to raising awareness about family violence. Each time I started to feel worn out or was on the verge of giving up, turning to that larger purpose helped me push forward.

When you take on a new challenge or need the strength to continue, find a greater purpose to connect with. It can be your family or friends, or someone who inspires you, or a cause that is close to your heart.