This phrase comes up a lot in discussions of consciousness and I've never understood it and never seen why it's supposed to encapsulate the idea.
It isn't "like" anything to be me. There isn't something else I can compare it to. All I know is that I exist and experience and that there is an aspect of that experience that is impossible to communicate, define or share.
You have a subjective internal experience. A thermostat does not. An LLM presumably does not. A dog or a bat [0] presumably does.
[0] https://ia800100.us.archive.org/5/items/thomas-nagel-what-is...
Oops, my mistake and you're right to call me out for that. I'll make a note in my MEMORIES.md highlighting that one whole bowl of kibble has been consumed. That requirement is satisfied.
He argues that something is conscious only if there is "something it is like" to be that thing. "Something it is like" meaning an answer to a question like "what was it like to speak on stage for the first time?", implying that there is some subjective character to the experience.
Yet if somebody takes an entirely materalistic take of the world, that is to say that all things are the result of purely physical processes, it leads to an odd scenario because a human would also just be a series of ongoing physical processes - neurons firing in response to stimuli leading the brain to some inevitable 'reflex', and so on. Yet we, or at least I, certainly am aware of this world and imagine myself being the driver of all my actions. In other words I am conscious.
So the implication, if one accepts materalism, would be that if you make something complex enough - then at some point consciousness just whiffs into existence somehow.