Business is usually conducted during the day, under the rising sun. With the sun overhead, it makes it harder for shadows to complete their assignments. Whether a village is full of civilians or guards, a true shadow will be able to find a way to remain undetected and complete the task at hand.
How a ninja is able to remain in the shadows in broad daylight displays their mastery of the art of assassination.
“I’m not here as an order. I’m here for somebody’s life.”
“Sorry, but if you’re here for mine, you’re not gonna get it.”
Luka's Notebooks 