'Darkness' in the Bible

I realized that wisdom is preferable to folly, just as light is preferable to darkness:

The wise man can see where he is going, but the fool walks in darkness. Yet I also realized that the same fate happens to them both.

Surely, he ate in darkness every day of his life, and he suffered greatly with sickness and anger.

Though the stillborn child came into the world for no reason and departed into darkness, though its name is shrouded in darkness,

So, if a man lives many years, let him rejoice in them all, but let him remember that the days of darkness will be many -- all that is about to come is obscure.