The reason we forget is that we don't actively remember.
Does that sound obvious enough? It should. Why do you make a list for the grocery store? Why do you make up an acronym for the three things you need from Walmart (E - eggs, B - baggies, B - bread, E-B-B)? Why do you frantically find the voice record on your iDevice to say something before it slips away and then email that to yourself so that you remember that you recorded it? Or is that just me?
Spiritually, we're great forgetters. If we're successful at one thing spiritually, that's it. But we're in common company. So were the Hebrews. This whole psalm is composed to rehearse the deliverance from Egypt and the resulting consequences - both good and bad - for that rescue. Asaph created the psalm and built in not forgetting into the text (v.7, 11, 42).
One of the reasons that the Spirit of God inspired this text is to remind us to rehearse the great things that God has done in our lives so that we don't forget. And more than that, so that we pass on the incredible deeds of God in our generation and the ones gone before us to our kids (v.6-7).
Around dinner tables. At lunch gatherings. During bedtime routines. When an event sparks a memory. And many more than I can mention.
Story-telling is active remembering.