宮沢賢治「農民芸術概論綱要」（1926年）より。文末に句点を補った。

I wonder if we didn't lost in translation, since it would have more sense as:

As long as the whole world has not reached happiness, individual unhappiness is possible.

I am not putting this comment on English sentence, since all languages, that I understand, says the same, and lot of them link directly to Japaneese.
I don't know Japaneese at all, just expecting visdom from them. Saying that no one could be happy because we are not all happy is kind a nonsense. Unless this is the joke, what I didn't expect. Just check it one more time, please.

I'm sorry. I haven't noticed this comment.

The English translation is correct.

個人 = individual
の = 's
幸福 = happiness
は = is
あり得ない = impossible

Even if it may sound like a nonsense, Kenji said it completely seriously. He seems to have been a committed altruist.

I guess this remark has something to do with the ideal of Mahayana Buddhism.

"The Mahāyāna tradition holds that pursuing only the release from suffering and attainment of Nirvāṇa is too narrow an aspiration, because it lacks the motivation of actively resolving to liberate all other sentient beings from Saṃsāra. One who engages in this path is called a bodhisattva. Bodhisattvas could reach nirvana, but they believed it was more important to help others on their path of finding nirvana rather than committing fully to nirvana themselves."
(http://en.wikipedia.org/wiki/Mahayana#Bodhisattva)

Thank you for a such good answer. It is worth waiting for. :)

I didn't know it has religious background, so me saying it is nonsense is somewhat offensive. I must be more careful with words I use. And, now, reading it, it doesn't seem wrong, all depends on the perspective with such deep, philosophical statements. One must go beyond the surface to find the true meaning.