Please check out the following sentences.
1. When class started, I suddenly realized that I forgot to do my homework.
2. My teacher was angry at my laziness and had me stand in front of the class.
3. How embarrassed I was !
- one thing happening before another, both in the past
- the two events being logically related.
- an absence of adverbs, such as "before, last night", which would make the past perfect unnecessary.