system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come, given we hear ourselves differently from how we think we sound, we can reproduce musical notes accurately by singing, just by ear?

I mean, shouldn't we be slightly out if we hear ourselves and think we've hit the note?

Same goes with mimicry, I guess... If we think we are replicating a sound of someone's voice, wouldn't it be different to everyone else hearing it?
gpt
So, there are sort of two different things going on here.

Nobody sings a single musical note, note really.  When we sing, speak, or play a note, there are a bunch of different pitches that blend together.  These give us the tone or *timbre* of the note.  The thing we think of as the pitch of the note is the lowest or *fundamental* note.

When we hear ourselves speak live vs in a recording, we don't hear a different note.  Instead, we hear a different *tone*.  The notes are the same, but the version we hear internally has more of the lower parts that make up the tone.  But the lowest note is still the same one.

TLDR: we hear ourselves sing the same note but with a different tone.  Harmonising is about the note, so the tone doesn't really matter.