When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Answer: riddle

More What am I ? with answers

More What am I ?

When you have me, you feel like sharing me. But, if you do share me, you don't have me. What am I?
When you take away the whole from me, there is always some left. What am I?
Where force can't get through, I with a gentle movement do. What am I?
Where there is light is the only place I can live. Yet if light shines on me I die. What am I?
While I'm a challenge for one and a rebuke between two, Yet I still have a direction for every number. What am I?
White, dark, round, square, big or small, I am seen on Valentine’s Day, and loved by all. What am I?
Whoever made me don’t want me. Whoever bought me don’t need me. Whoever use me don’t know me. What am I?
Whoever makes it, tells it not. Whoever takes it, knows it not. Whoever knows it, wants it not. What am I?
Whoever makes me, tells me not. Whoever takes me, knows me not. Whoever knows me, wants me not. What am I?
With a halo of water and a tongue of wood, stone as skin long I stood. What am I?
With me you are blind, To others and what they are, Over me you cannot see, Even though I'm in your head, I am full of myself, I think I'm better than you, I'm a horrible thing to be, Can you tell me, What am I?
With no hammer or any kind of tool I build my house so quickly. What am I?