Data.Either.Validation monoid implementation, ok+error=ok?

I look at this:

http://hackage.haskell.org/package/either-5.0.1.1/docs/Data-Either-Validation.html

implementation of monoid:

instance Monoid e => Monoid (Validation e a) where
  mempty = Failure mempty
  Failure e1 `mappend` Failure e2 = Failure (e1 `mappend` e2)
  Failure _  `mappend` Success a2 = Success a2
  Success a1 `mappend` Failure _  = Success a1
  Success a1 `mappend` Success _  = Success a1

I expect that success with error must be merged to error... and can't understand why it implemented in such a way that success with error merged to success?

So if I have a bunch of validation results and one of them is failed I expect to reduce all to fail, with merging all errors.

but:

Prelude Data.Either.Validation> Success 1 `mappend` Failure ["er1"] `mappend` Failure ["er2"]
Success 1

why?

comes to mind, if I have several validation results and if one of them pass - then total validation ok.. for such cases? for, example if I validate that contact is email or skype or phone, one of them valid, then it's ok?