Answer:
I can ruin your day, or darken your life. And while I'm expected, I'm never alright. I'm bad for business, and worse for your hair. Wherever I am, there's something not there.
What is it that given one, you’ll have either two or none?
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What an fill a room but takes up no space?
What has to be broken before it can be used?
You use it between your head and your toes, the more it works the thinner it grows.