Can we guarantee there is a function with low in sample error in H

[pouramini]

There is this sentence in book, page 25

We cannot guarantee that we will find a hypothesis that achieves Ein (g) ~ 0,
but at least we will know if we find it

My English is not perfect, what does it mean? does it mean that we only should find such a function, otherwise there is no way to know if it exists?!

[htlin]

Whether there is some with depends on the hypothesis set. So we cannot always guarantee finding a with low .

[pouramini]

Thank you!