Our Cavemen have been taught that the Four Components of Distance Running are Endurance, Strength, Speed, and Guts. Every workout we do helps us improve at least one of these components. We do all of our runs, including our capillary runs to improve our endurance. We do hills and weightlift to increase our strength. We do fartlek and interval workouts to improve our speed. But, guts is the one component that must be developed alone by each runner; it is a conscious decision to get up when one has fallen, to push on when one hurts, and to persevere when one is behind. The word that defines this internal drive, this toughness of spirit, in the Finnish language is SISU. This word will be on the back of our team shirts this year to help remind us of the fourth component of distance running which we need to reach our running potential.
Here is a link to a great article on Sisu in the March, 2013 Runners World.
Here is a great video of Lasse Viren's amazing race in the 1972 Olympics, where he was tripped, got back up, and won in world record time.
Viren then went on to win the 5000m Run a week later, and then won both races again at the 1976 Olympics.