* The sun's light overwhelms them: The sun is incredibly bright, and its light scatters in our atmosphere, making it impossible for us to see the fainter light of stars during the day.
* They are always there: Stars continue to shine 24/7, even when we can't see them because of the sun.
Think of it like this: Imagine you're in a brightly lit room. You can't see the fireflies outside because the room's light is too strong. But the fireflies are still there, just out of sight.
