First of all, they believed that they would get out, they had faith that one day they would be free.
They would get to see their family, their friends.
And this faith kept them going.
At the same time, and this is the second component, they had realistic beliefs and evaluation of the situation.
If any one of these two components were missing, they were unlikely to survive.
If they didn't have faith and they didn't believed it they would survive, they were very likely to die in the harsh conditions.
On the other hand, if they thought that they would get out by this coming Christmas,
and really believed that they would get out by this coming Christmas, they were also less likely to survive.
Because they didn't get out by this coming Christmas, and then they were desponded, resigned, helpless, and very often, they died.
So it was the two components,
believe that you would get out, but at the same time know that you need to deal with reality and that it's tough.
Here is what James Stockdale said,
"you must never confuse faith that you would prevail in the end which you can never afford to lose
with the discipline to confront the most brutal facts of your current reality whatever they might be."
Now the thing is that you may be wrong at times. And sometimes you may really believe in something,
and believe it that you have realistic expectations and not succeed.