Sometimes, there are more than two events. When this happens, you need to bear in mind that the event that took place further back in the past always takes the Past Perfect tense.

The ones that are closer to the present, go in Simple Past, like this:

When I got to the party, I realized I had forgotten my purse

Again, time markers help you clarify the sequence of these events:

1) I forgot my purse 2) I got to the party 3) I realized I had forgotten my purse