Why did Narcissus die?
It's a question anyone can easily answer.
Because he loved himself.
Buddhism therefore advises anattā (non-self). Narcissus accelerated his suffering because he loved 'him-Self'. The causes of his death were due to the three poisons that led him to have but to loving 'him-Self'.
There, the three spiritual poisons are, 1) a black pig for ignorance, 2) a green snake for envy and hatred and 3) a red cock and for lust and greed. They go round and round with a bite of tails to tails without breaking.
It's Wheel of Life.