Some of you think it's crazy, but actually, it isn't! It's completely true!
Our brain can store unlimited memories. So, if some event occurred in the past, it's still stored in your brain, even if it happened years ago! The only problem is that you just don't remember it! When that event occurred, a link was created in our brain that made us remember when this event occurred, that happened at that event, and where it occurred.
Whenever we try to remember it, that link made us remember that event! If you forget that event, don't worry, it's still stored in your memory! The problem is the link which made us remember that particular event, got broken. If we get a little hint of that event, for example, where it occurred, I'm sure we all slap our thigh, and say, "now I remember!"
When that hint was given, the broken link got connected again and you remember that event.
So, as you can see, god has created our brains an unlimited storage place in which we could store unlimited memories! We should thank god for all the blessings he has given us.