Dice que tenían... mucha capacidad o mucha voluntad, mucha fuerza.
Say that they had... a lot of capacity or a lot of will, lots of strength.
Captions 39-40, Rafael T. - Guatemala HermosaPlay Caption
Rafael T. obviously enjoys telling tales of his beautiful (hermosa) country, Guatemala. In this video, he tells us the tale of a mountain called Cerro de Oro that, back in the day -a hundred or so years ago- his ancestors managed to move inland from the coast. How did they manage to accomplish that? "They say they had a lot of capacity or a lot of will, lots of strength..." Rafael explains in captions 39-40. But despite their remarkable fuerza de voluntad ("willpower"), it turns out they were unable to move the mountain as far as they were aiming for. So, as you can see, in legends and reality, voluntad is a word to describe an intention, wish or will, but not necessarily an accomplishment.
On a related note, por mi propia voluntad -meaning "of my own free will"--is a common Spanish phrase that makes voluntad's tie to the English word "voluntary" easy to see.