There are known knowns - things we know we know.
There are known unknowns - things we know we don't know.
And there are unknown unknowns - things we don't know we don't know.
Where would we be without the wisdom of Donald Rumsfeld?
As a consultant I have two primary uses - to help clients find their 'known knowns' and 'known unknowns' (and work out what to do about it) and to spot the 'unknown unknowns' coming. I'm not psychic but the value of experience (and expertise) in the projects I work on means I can see the potential risks and challenges coming. I know what should happen (and when) and what might happen (and in most cases how to avoid the negative implications).
I liken it to jumping off a cliff. New ventures, projects, call them what you will, are scary. They're the unknown unknowns. I know the project might look to you like we're jumping off a cliff. And we are. But I've jumped off this particular cliff before. Sure, the weather is different and I've never jumped off it with you but I know the equipment we need and the safe space to land. You can stand there and admire the view if you want but you needn't be afraid. We can take the risk and make a safe landing together.