Essentially, life can turn out to be both a gift and a misfortune.

But we are not contrasting "misfortune" with a "gift," but rather with a challenge. And a challenge is not a misfortune; it is a tool for gaining knowledge.

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However, it seems to me that in life, there is a diametrically opposite trend...
We are born, and we die: we are given the happiness of living a life, and then, when it is sad to part with it, it is taken away...
This is doubly upsetting...

What diametrically opposite trend are you talking about? What does death have to do with it? Is death observed in life? Firstly, death ends life, and is not one of its events. Secondly, if we are not talking about violent or premature death, it is far from always the case that the dying person so desperately wants to live. Many people in old age look forward to death, and sometimes, considering that their tools for experiencing life are either unable to function or are not being used, their desire is quite understandable.