请用 look back造句解释下什么时候出现look back on 和他们的区别,可以在这个基础上再讲点么?

两个都有回顾的意思,只是look back多了一个回头看的意思
look back
回头看
例句:
Looking back the way we had come,we could see the whole valley spread out behind us.
回头看来路时,我们可以看见整个河谷展现在身后.
look back on
vt.回顾(追想)
例句:
I still shudder when I look back on the past.
想起过去,我仍然不寒而粟.
I like to look back on my high-school days,which were the happiest in my life.
我喜欢回顾我的中学时代,那是我生命中最快乐的时光.
She can look back on her career with great satisfaction.
她回顾自己的经历觉得心满意足.