system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that i can't remember the lyrics to part of a song but if i sing the song in my head, it just comes to me without even thinking?

I can just sing along from the beginning and remember the lyrics without even thinking about, it just comes to me right on cue.
gpt
Memory is still very poorly understood by experts and thus any answer is going to be based on theories which may seem good now, but as we learn more we are likely to change our understandings radically.

We don't store pieces of information in a single place to be activated when we want to recall it later; information is stored in relation to other networks of ideas. This can be abused for our enjoyment like asking someone to answer questions about white things and then asking them what an adult cow drinks and the answer will usually be 'milk' as milk is part of the 'white' network in the brain. Another fairly well-known consequence is that when you learn information in a particular environment (say a classroom), aspects of that environment become part of the relational networks for that information you learned and people tend to be able to recall the information better when they are asked to in environments similar to that where the information was learned.

As for a song, each part of the song is learned in relation to the bits which came just before it and that becomes part of the network which allows you to recall it. Music generally activates parts of your brain which are not active when you are simply learning or recalling language, so recalling lyrics without activating the other rhythmic and emotional networks associated with the music is even more difficult. The more networks a piece of information is associated with, the more difficult it is for your brain to recall it when some of those networks are not being activated and even if you succeed in recalling parts of the memory, that act is likely to begin to activate those other networks, so if you start recalling lyrics, you might have to put effort into *not* activating the networks related to the song and singing it in your head. You can see this when people start to recall a song or poetry and they begin to speak rhythmically even if they don't really want to.