In Naruto Shippuden episode 359 around 11:47, before the Uchiha massacre, Itachi meets Obito (camouflaged with a mask as either Tobi or Madara) in the forest. Obito tells Itachi to keep his eyes closed while killing the Uchiha people and Itachi agrees saying "I don't have any other choice!".
Why does Obito tell Itachi to keep his eyes closed, and why does Itachi obey?