grammar - How are these two sentences not negating their premise?

In my JLPT textbook, 日本語総まとめＮ１読解, on page17, there are these two sentences (which are both part of a larger paragraph, but I hope I have included enough):

自分{じぶん}なんかにできるわけがないとあきらめる態度{たいど}ほどじれったいものはない

それ以上{いじょう}は望{のぞ}まないというような考{かんが}えの人{ひと}が少{すく}なからずいるのは残念{ざんねん}でならない

A translation for the first sentence is offered in the book, which is, "it is very frustrating to see people giving up on things even before they start." There is no translation given for the second sentence, but it is clear from the lesson it is being offered in that it is saying something like, "it's disappointing that it's no small number of people that think they won't hope for more."

Both sentences seem to be asserting something. That it is frustrating that people give up on things and that the number of people who don't hope is too many.

But when I read the sentences, they seem to me to be negating those premises because they end with ものはない and でならない. My reading of them is "it isn't very frustrating to see people giving up on things even before they start," and, "it's not disappointing that it's no small number of people that think they won't hope for more."

Me and the book disagree on whether these sentences are positive or negatve assertions, but I assume it's me that is mistaken somehow.

How is it that these sentences are not negative, in spite of ものはない and でならない?

Answer

The key to the first one is in the fact that it all comes down to ～ほどじれったいものはない. It is a negative sentence, but it's not negating the meaning of the sentence. If we put it into English it means "There's nothing as frustrating as seeing people give up on things before they start." And that's if we use the book's translation for the rest of it. The point is that the speaker is presenting this situation and trying to find something worse than that, and saying that such a thing doesn't exist. It's like saying "Murder is bad" vs. "There's nothing as bad as murder." The latter isn't suggesting that murder is good.

As for the second one I am curious to see how you would parse the meaning of this since it seems that you're missing the phrase ~てならない, which just that means something is unbearable, or at least felt very strongly. The fact that the verb ends in ない doesn't mean we're inverting the meaning of the sentence. On the contrary in this case it's making the meaning even stronger. So in this case the speaker is not saying that it's not disappointing but that it's unbearably or extremely disappointing. Compare this to the phrase ～てたまらない.

See here for examples.