During his walks, he often loses himself in reflection about his past.

reflection 来自动词 reflect（反映、思考），加上名词后缀 -ion 构成。reflect 由前缀 re-（表示"重新"）和词根 flect（表示"弯曲"）组成，原意是"光线反射"，引申为"思考、反省"的意思。reflection 在这里指"沉思、反省"的心理活动。