过去是还没长大的坚强想念是还没成熟的过去
[guò qù shì hái méi zhăng dà de jiān qiáng xiăng niàn shì hái méi chéng shú de guò qù]
It implies reflection on growth where one's toughness and nostalgia are related to their maturing process and looking back at the younger version of themselves through the lens of memory, with sentiments tied up with the past.