Iron K. Tager wrote:
If you can remember it, was it really worth remembering? I'm sure you have some memories you have no practical use for in place of things you wish you could remember.
They will all come back to me in time, they always do.

Yes, but the memories that immediately come to mind when you think of a particular topic are the ones that usually seem to be the most vivid memories of that topic.
For example, if someone said to me:
"Hey, do you remember when you used to go to camp in the summer?"
Only the most vivid memories of my years going to summer camp are the ones that I can recall without further prompting.
However, of someone had said to me:
"Hey, do you remember when we did X at summer camp?"
I would likely remember whatever it is that X is supposed to be, even if I otherwise would not remember it.
Most of the time, memories are just a highlight reel, consisting of different topics, such as camp, school, work, or vacation to name a few; and in those topics, only the most vivid (I like the word vivid) memories for those topics are readily available to our minds, however with further reflection on the topic, or with a little outside assistance from something like a picture, or a conversation, just about any memory can be recovered.
Every memory has some useful purpose, even the bad ones, and the ones that seem to serve no purpose. In fact, I find the seemingly useless information that is gathered over the course of one's life to be the most useful information of all.... like pi. Everyone should know pi.