It is because you believe things are permanent. When a flower dies, you don't suffer much, because you understand that flowers are impermanent. But you cannot accept the impermanence of your beloved one, and you suffer deeply when she passes away. If you look deeply into impermanence, you will do your best to make her happy right now. Aware of impermanence, you become positive, loving and wise.
Impermanence is good news.
Without impermanence, nothing would be possible. With impermanence, every door is open for change. Impermanence is an instrument for our liberation.