In any given plein-air painting of a few hours, you can probably only capture one percent of the detail that meets your eyes.
There have been some amazing attempts to capture more with extended periods of close observation. The PreRaphaelites tried to follow John Ruskin’s advice in his influential treatise Modern Painters in 1843. Ruskin suggested that artists should to “Go to Nature in all singleness of heart, and walk with her laboriously and trustingly, having no other thought but how best to penetrate her meaning, rejecting nothing, selecting nothing, and scorning nothing.”
In other words, go for the 100 percent.
Here’s a closeup of William Holman Hunt’s Hireling Shepherd (1851), where he lovingly painted the tiniest blades of grass. The level of detail creates a haunting, dreamlike quality, and everything is imbued with symbolic meaning.
Assuming that not many of us have the time or patience or desire for such infinite exactitude, the question is WHICH fraction—which one percent—of the immensity of Nature should we try to capture?
When Daniel Robinson set out to paint this beached sailing ship he had a hierarchy of interest. With the limited time he had to paint the scene, he had to “reject, select, and scorn” a lot of details. He scrubbed in the grass as a flat tone and did the same with the beach, the far mountain, and the sky.
Instead he lavished his attention on the ship’s standing and running rigging. He most likely used a small sable brush (either a round or a rigger brush) with his hand steadied with a mahl stick. He painted what interested him the most and simplified the rest.
It’s a completely different aesthetic from what Ruskin advocated. The point is to convey a feeling of completeness, selecting only the one percent that interests you.
For a deep analysis of Holman Hunt's Hireling Shepherd, check out the Victorian Web Book and the Wikipedia entry about the painting.
For Ruskin's quote in context, link.