I'm having trouble understanding the difference between The Past Simple and the Past Perfect in some cases. I've hust read that there's no need to use the Past Perfect when the sequence is clear. The problem is I don't understand what makes the sequence clear. Is this sentence correct?
She lazily leaned against the chair that he bought for her.
I'm sure that it's obvious that he bought the chair before she leaned against it. Am I right?
But can we say "She lazily leaned against the chair that he had bought for her"?
It this sentence correct or is it completely unnecessary to use the Past Perfect in this case?
What about "He read the diary of a student that (had) committed suicide"? I think it's obvious that the student committed suicide before someone read his or her diary. So, do I really need to use the Past Perfect in this case?
I don't get it. I can't understand what exactly makes the sequence clear for a native English speaker.