Sisu is a Finnish concept that describes a stoic resilience, determination and hardiness. It's considered necessary to face the difficulties of life in general and in particular, of life in harsh conditions.
It roughly translates as strength of will, determination and perseverance. There is something so starkly similar between this concept and that of a river stone. After a rock is dislodged from it's home, it gets bumped around, subject to the natural forces of wind and water. It gets banged around against other rocks, suffering damage with each impact, often loosing pieces of itself. The process known as 'weathering'.
However, it perseveres. It loses its jagged edges and it becomes smooth and round. Soon it settles into the river bed, no longer being bothered by the flow of water, but embracing the way it continues to smooth it's surface.
Sisu isn’t momentary courage, but the power to sustain that courage to see something through.