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. Having lived here for most of my life, I believe that sisu plays a significant role in our well-being and ability to maintain such a positive and resilient mindset.

As a psychology expert, I've devoted my career to teaching people how to incorporate sisu into their lives. Here's my best advice:

1. Find a purpose outside of yourself.

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.

2. Increase resilience through training.

Leading up to the run, I trained nearly every day for two years. I laced up my running shoes even when I didn't want to. I always showed up, rain or shine.

Practice and preparation makes it easier to harness our inner sisu. Studies show that our bodies have hidden reserves that it naturally draws upon when we need them most. So the more we challenge ourselves, the more we pick up on habits that bolster our resilience.

Focusing on my breathing to calm my nervous system was the strategy that improved my running. Over time, I went from a beginner to clocking in 10 to 15 miles a day.

3. Be gentle with yourself and connect with nature.

I used to think that in order to be successful, I had to be hard on myself. But there's a limit to how far you can go if you don't balance toughness with compassion.

I got injured once during my training period. I had been running 30 miles a day for 12 consecutive days. I had to ask myself whether to quit or push myself even more.

But I decided on a third option: I let my body heal. Even if I slowed down, I could still meet my 1,500-mile goal by incorporating cycling into my trek.

And since I was no longer trying to meet a breakneck pace, I got to spend more time appreciating the beauty of the landscape around me during my expedition.

In Finland, walking and hiking in nature is a core part of our culture. It helps us find an inner calm and sense of happiness that serves us during hard times.

E. Elisabet Lahti, PhD, is a psychology expert and pioneering researcher of "sisu." She is the author of "Gentle Power: A Revolution in How We Think, Lead and Succeed Using the Gentle Art of Sisu." Born and raised in Finland, she holds master's degrees in social psychology and positive psychology. Follow her on Instagram and Facebook.

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