In my life I have never got farther, nor will I get farther, than ‘fear and trembling’, that point at which I am literally quite certain that everyone else will easily attain the bliss of heaven, and only I shall not. . . . Telling other people. . . ‘You are eternally lost’ is something I cannot do. As far as I am concerned, the situation is that all the others will, of course, go to heaven; the only doubt is whether I shall get there.
Soren Kierkegaard, quoted in Hans Urs von Balthasar, Dare We Hope "That All Men Be Saved"? 2nd edition (2014) chapter 5
Dare We Hope is mainly about our knowledge—or more precisely our certainty—regarding the eternal destiny of human souls, whether our own or those of others. This is something about which Christians widely disagree, but the Catholic position (and therefore mine) is that we cannot have complete assurance either that we are saved or that any other particular person is damned. Regarding the latter, one recent catechism puts it as follows:
Neither Holy Scripture nor the Church’s Tradition of faith asserts with certainty of any man that he is actually in hell. Hell is always held before our eyes as a real possibility, one connected with the offer of conversion and life.
The Church’s Confession of Faith: A Catholic Catechism for Adults, published by the German Bishops’ Conference, English edition (San Francisco: Ignatius Press, 1987), p. 346