想到这里我就理解大人们的一片苦心了。

I fully understand this situation thinking about this.

我很欣慰，你终于理解我的一片苦心了。

I am relieved that you have at last seen my painstaking .

居了，你可不要辜负人家的一片苦心啊，要不然我可饶不了你。

Reside, you didn't want to be ungrateful to the someone else's one with patience, otherwise I can Rao not you.