He knows it doesn't matter; or not much anyway, but once when they were kids, Itachi and he were out in front of the Uchiha home.
Itachi, on his father's instructions, was lazily hosing down the front steps to the entrance while Sasuke scuttled back and forth between the porch and the garden, gradually collecting a small pile of colorful stones from the thin stream that trickled through the front yard. He laid them out to dry in the sun, thinking that he could show them to his mother later. Itachi called Sasuke over for a moment and he obediently dropped the stones, rubbing his dirty hands on his shorts as he ran over.
"What is it?" he asked eagerly, hoping that Itachi would show him a cool fighting move or something of that caliber.
Itachi held the hose out. "Look," he said.
He pressed his thumb over the nozzle of the hose, and the water, instead of slugging out in great gulps, suddenly burst through in a dazzling fan of droplets.
Sasuke's eyes widened in awe, realizing that he could see a rainbow inside the water. It was like a secret floating in air.
After a few moments, Itachi casually took his finger off and the misty rain once again became a spout. The rainbow had disappeared.
Sasuke looked up at his older brother in wonder. "Where did it go?" he asked.
Itachi paused, smiling gently at the look in Sasuke's eyes. "Come here," he said, crouching down. "I'll tell you."
Sasuke cautiously stepped forward, ambling towards Itachi's beckoning hand. However, when Sasuke got within a foot of his brother, Itachi suddenly angled the hose so that Sasuke got a cold blast full in the face.
"AH—nii-chan!" he exclaimed in shock and annoyance, scrubbing furiously at his sopping wet face as Itachi laughed genially, shoulders shaking. "I—that wasn't funny! I'm telling Mom!" he cried, and turned, running toward the kitchen, trying not to slip on the wet patches.
He can't explain why, but when Itachi's bloody fingers poke him in the forehead that last time and he falls, this is the only memory that flashes through Sasuke's head.
Fin
Family dynamics are important to me. It's so tragic to think of two kids just being kids but having such a cruel future.