Hi @pavelnedobity, thank you for your question, it is a difficult question. Some people become sick and eventually die after some suffering, others die young in an unexpected accident, some die peacefully in their sleep, we don't know why things happen like that. I think @stardust gave a good explanation. A sudden death of a loved one for instance can teach us that life can end unexpectedly and ask the question are we ready to die and meet our creator. To suffer can also make us stronger as a person and make us to grow personally.
Thank you for your question.