从未知道放弃后会很后悔
[cóng wèi zhī dào fàng qì hòu huì hĕn hòu huĭ]
This implies the person made a choice without fully anticipating how they'd feel afterwards, perhaps having given up too soon on something meaningful. Now they regret that past decision because the results were not what they expected and there was so much untapped potential.