One possible version：
Dear Jack,
I hear you are in low spirits. I feel very sorry for you.
Life is not always smooth. We have to learn to take the bad with the good. So, you should take a positive attitude towards life. There are so many people with disabilities who are still fighting for their dreams. Please don’t lose heart. There is a saying, "Nothing is impossible for a willing heart." Just remember that nothing in the world is too difficult if you put your heart into it. Only in this way can you regain your hope for a beautiful life in the future.
I look forward to hearing good news from you!
Yours,
Li Hua

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