One possible version

Dear Li Ping,

I’m glad that you trust me so much and tell me your true feeling, now I’ve read an article which says that it is important to be friendly to yourself first and then to others, and gives us a few tips, such as forgiving yourself, realizing your virtues and not comparing with others.

As is known to all, no one is perfect, and everyone has their own strength and weakness, so if you fall behind others in some aspects, it’s natural and there’s nothing so serious for you as to feel frustrated.

I know you’re worried about your study because you’ve not got as good results as others in the exams, but that’s not the most important, so long as you try your best, I’m sure you’ll make progress. Besides, you have your own virtues which some others don’t have, for example, you play basketball better than many other students in our school, and you also play the guitar well. If you know how we envy you, you will not feel so bad!

So never feel discouraged /inferior if you fall behind others temporarily in your study, just believe in yourself.

With the best wishes!

Yours truly

Li Hua