Suddenly remembering things you were trying to remember

What causes this phenomenon:

You are sitting there trying to remember something, but you cannot recall it. You think “it begins with ‘b’” (or whatever) but that’s the best you can do.

Then all of sudden, three hours (or days) later, when you are not even trying to recall it, it pops into your head out of the blue (making you exclaim, “oh yeah, that’s it!”), with seemingly no provocation.

Side question:

How come, occasionally when we try really hard to recall something, we can sometimes know “it begins with ‘b’”, but not recall the term or name in its entirety?

If our brain knows it begins with ‘b’, why can’t it return the rest of the word?

This truly is a remarkable human trait, isn’t it? I’ve heard it referred to “ambient thinking”, and is also related to the “tip of the tongue” phenomenon, especially with your example of knowing SOMETHING about the topic, but not being able to eloquently explain your thought process. Wikipedia has a nice articleabout the tip of the tongue phenomenon, if you haven’t had a chance to check it out. Really fascinating stuff, the human brain!

There’s an analogous thing that happens in your eyes known as Averted vision - Wikipedia which I can’t help but believe involves similar brain functions.

All I can say is that I know it works! I never despair that sooner or later whatever I’m trying to remember (and having no luck with in the “straining to recall” mode) will just pop into my awareness. It’s happened more times than I can count. Only a few things just never come back. I treat such failures as having been too faint to matter.

Just recently I was trying to recall the names of my grammar school teachers. They still lurk in the recesses of my mind that I can’t access. But I have been able to remember most of my schoolmates! Go figure.

IANA neurologist or psychologist, but as I understand, the brain tends to “file” things that are similar near eachother. As such, I might liken the process to having a bunch of messy piles where you know you left a certain paper in a certain file, but you look through the stack again and again but can’t seem to find it.

That is, you don’t always get a direct link of “actor in this movie’s name is X” because you haven’t really strengthened that neural connection, instead you get a series of weaker connections akin to “his name begins with B”, “he was also in Y”, etc. It all just depends on how you liken different things together.
At least for me, I’ll sometimes get the first letter, but more often I’ll get other parts of the word, specifically the rhyming part, or something related to it. For related, it’ll often be “it’s like the opposite of X” or “it’s somewhere between Y and Z”. I actually dislike the “It starts with B” because it seems like either it’s just flat-out wrong or my brain just doesn’t sort like that so it’s more of a hinderance. In other instances, I’ll actually have the specific word I want but not really “grab onto it” and then get stuck looking for it.

Bah, gonna miss the edit window. Anyway, as for why it comes up later, it’s probably because you’re somehow accessing it in a round-about way, it just doesn’t seem like there’s any direct correlation. For instance, using the same sort of actor scenario, you were looking for a guy with a B name in movie X and Y, but you don’t find it. Later, you see a commercial for beer that has a scene in a bar, and one of those movies, or maybe even a completely different one, has a scene that you connected him to a bar and it comes back up and you make the initial connection. You may or may not even be aware of that alternate connection, but that’s one way.

I suppose it’s also possible that you somehow “keep looking” in the background and maybe come onto it once you’ve had time to process it more, but it’s sort of hard to tell whether it was just further searching or some alternate connection, so I have no idea which one is actually more how it works without a neurologist checks in; this is more from an AI perspective of how we programatically achieve the same sort of thing.

In my mind, that seems to be true, because this is almost always how that “Oh, yes, that’s what it was” feeling happens for me. I’ll manage to recall something associated with the forgotten thing, and bing! the connection gets made and suddenly I can remember the name, title, color, date, or whatever it was I was trying to.