What is the difference between the sentence "He was tired because he was exercising too hard" and "He was tired because he had been exercising too hard"?
1 Answer
The first one implies he was still exercising at the time he was tired. The second implies he was tired after exercising. It's a subtle difference but it's there.
Grammatically it's the difference between past tense vs past participle, but you probably don't need to know that.