God/goodness/Heaven knows phrase spoken informal
No one has an idea.
God knows what happened to them.
God knows how long we'll have to wait here.
It is unquestionably true, certain, or certain that; it is clear that.
Goodness knows my plane is feasible. You can believe in me.
Heaven knows you were planning to go without me.
A legal matter that is very easy to solve
State something in a very strong, clear and effective way
To know powerful and influential people who can support you
Don't make plans that depend on something hoped before it has actually happened.
Don't make sure that the result will be good until it actually happens.
You should not make sure anything before you actually win the first prize. Don't count your chickens before they are hatched. Everything can happen.