Q:

Why was it a good thing that hope remained in Pandora's box?

One thing has always confused me about the story of Pandora. When she opened her box (or jar, whatever), all sorts of evil things escaped outside the box, and this is why we have evil in the world now. Then, she closed the box before hope could escape, so that hope remained within the box. 
Does this mean that the world doesn't have hope, though (since it's still stuck in the box)? I thought that the "moral" of the story, so to speak, was that even though there's all this evil out in the world, there's still hope, so not all is lost. But that doesn't make sense if hope is still stuck inside the box.

A:

Πανδώρα (παν + δώρα): the all-gifted
Etymology of Pandora

The myth of Pandora (the first mortal woman) is misinterpreted. I've seen many modern books wrongly claiming that hope did escape the box and, despite all evil that was spread throughout the land, people still hoped that better days would soon come.
Hesiod is the one that refers to the box (it was not a box actually, but more like a jar) and claims that Pandora (actually referring to women) is the root of all evil, because she would hurt the man with her beauty and lies.

For from her is the descent of female women       
a great pain for mortals, living with men, 
companions not of destructive Poverty but of Plenty.
Theogony

When Pandora opened the box, all evil escaped it, but Pandora (under Zeus' will) held hope inside the jar by closing the lid. Isiodus doesn't say why hope stayed into the jar, but one (judging from Isiodus' view on women) can imply that  he meant by that, that the men would have no hope against women, for without her, they would die alone, but with her, they'd have to withstand their cunning nature.
Judging by this, which is how Hesiod closes Theogony:

Thus it is not possible to escape the mind of Zeus.
Theogony

and

an angry Zeus decides to give humanity a punishing gift to compensate for the boon they had been given. He commands Hephaestus to mold from earth the first woman, a "beautiful evil" whose descendants would torment the human race
Wikipedia

One can see what Hesiod wanted to say in the end.

A:

Only Hope remained there in an unbreakable home within under the rim of the great jar, and did not fly out at the door.
Trans. Evelyn-White. 

The answer to this question depends on how you interpret the above quote. Is hope being protected in the jar? Or withheld from humanity? The word Hesiod uses for hope, elpis, can also mean 'expectation'. Verdenius states that "elpis may be regarded either (a) as a good, or (b) as an evil". In this view, the hope in Pandora's jar is potential, but for good or evil Hesiod never specified. 
Additional sources:
West, M. L. Hesiod, Theogony, ed. with prolegomena and commentary (Oxford 1966).
West, M. L. Hesiod, Works and Days, ed. with prolegomena and commentary (Oxford 1978).

A:

This is indeed confusingly presented but the implication is that Hope did not escape ("fly out the door").  One of the Aesop versions may clarify somewhat:

"Zeus gathered all the useful things together in a jar and put a lid on it. He then left the jar in human hands. But man had no self-control and he wanted to know what was in that jar, so he pushed the lid aside, letting those things go back to the abode of the gods. So all the good things flew away, soaring high above the earth, and Elpis (Hope) was the only thing left. When the lid was put back on the jar, Elpis (Hope) was kept inside. That is why Elpis (Hope) alone is still found among the people, promising that she will bestow on each of us the good things that have gone away."
Aesop, Fables 526 (from Babrius 58) (trans. Gibbs) (Greek fable C6th B.C.)

