Why did the healthy duckling suddenly die?

Probably because I moved, I was not used to life and died of depression; Or think that it is not its home, that you bought it, that it misses that hometown, becomes lovesick, and then dies; Or is it because you put it in a small yard, the night is dark and windy, plus heavy rain, your heart beats faster and you die suddenly ... There are too many reasons, brother (or sister? ), can you stop obsessing?