How can hope and despair be akin?

[davem]

From the Athrabeth:

'What is hope?' she (Andreth) said. 'An expectation of good, which though uncertain has some foundation in what is known? Then we have none.'
'That is one thing that Men call "hope",' said Finrod. 'Amdir we call it, "looking up". But there is another which is founded deeper. Estel we call it, that is "trust". It is not defeated by the ways of the world, for it does not come from experience, but from our nature and first being. If we are indeed the Eruhin, the Children of the One, then He will not suffer Himself to be deprived of His own, not by any Enemy, not even by ourselves. This is the last foundation of Estel, which we keep even when we contemplate the End: of all His designs the issue must be for His Children's joy. Amdir you have not, you say. Does no Estel at all abide?'

Its perhaps a problem with the 'translation' of Aragorn's words - both Estel & Amdir can be translated as 'hope', but while Amdir & despair can be 'one' in certain circumstances, Estel & despair cannot...