How did he do that? He had to live with the worst of circumstances, but he still had hope.
For some reason this hit me afresh today. Mormon lived his entire life surrounded by wickedness and war, but he remained faithful to God throughout it all. I can tell by his writing that he struggled with great discouragement over this situation and tried his hardest to change that. When he realized his circumstances would not change, he looked forward to the far distant future that God showed him in a vision. He was shown us, in our day, and though he saw similarities with his time, he felt hope and took an opportunity to reach out to speak to me – and you – to give us comfort,  reassurance,  and instruction to help us get through it.
Mormon 5

9 And also that a knowledge of these things must come unto the remnant of these people, and also unto the Gentiles, who the Lord hath said should scatter this people, and this people should be counted as naught among them—therefore I write a small abridgment, daring not to give a full account of the things which I have seen, because of the commandment which I have received, and also that ye might not have too great sorrow because of the wickedness of this people. 10 And now behold, this I speak unto their seed, and also to the Gentiles who have care for the house of Israel, that realize and know from whence their blessings come. 11 For I know that such will sorrow for the calamity of the house of Israel; yea, they will sorrow for the destruction of this people; they will sorrow that this people had not repented that they might have been clasped in the arms of Jesus.