Falling red is not the derivative meaning of turning ruthlessness into spring mud to protect flowers. It means that even if you have experienced setbacks and failures, you should turn these experiences into nutrients for your growth and make yourself stronger.
Falling red is not heartless, but turning into spring mud can protect flowers. It was originally a poem in the Tang Dynasty poet Bai Juyi's "Farewell to Ancient Grass", which means that even if the leaves wither, they can provide nutrients for flowers and plants.