We typically experience the act of forgetting, or more precisely, failing to remember, constantly as we get older, and have more and more things to forget.

Consider carefully what the act of remembering actually is. To greater or lesser extents, memory is stored experience - and by remembering something, we re-experience it. Sometimes, perhaps a small, particularly abstract thing... sometimes much more. Physically, vast and hugely diverse parts of your brain are affected by every experience, both internal or external. These aren't just recorded, like a computer records them. They are like echoes. They resonate. Putting something in that resembles them gets them back out. That's recognition. And we are flexible in the way we recognize things - that's representation, association... and ultimately, "rational thought." And on our own, in quiet moments, memories return on their own, unbidden, just like the action of tides and waves. We are in some ways just slaves to our experiences.

Trying to remember something, however, becomes a thing unto itself. Especially if we are neurotic about it - if we punish ourselves for being forgetful. So by trying to think about something, we are not actually thinking about it, because we are trying to think about it instead. In this way, our anger or apprehension with ourselves for forgetting... and our surprise, when we are finally reminded, and have a distinct feeling that it was in there all along... we just couldn't find it... That's because your mind is not a machine, as much as we sometimes might wish, or others might wish of us. Don't forget, that's sometimes a useful metaphor, but can be harmful.