Can I get that done?
Well I should be able to.

Can I make that be a success?
Well I think I could.

Can I make that actually work?
Well I might be able to.

Are you sure you can do this.
Erm.. I hope I can.

Are you sure you are up to the task.
Erm.. I am not sure.

Are you sure you can see it through.
Erm.. I doubt so.

Can you do anything at all.
Sigh. I can't.

Does that not make you useless?