Why do some singers sound good despite missing lots of notes and others sound awful when they just barely miss a note?

One can miss notes and still be in key. If the guitar player hits a F and the singer hits a G and it's in the same key and scale then the singer technically missed the note, but still sang in key. That's musically acceptable. It's when people sing out of key that it'll sound horrible.

fluidity, as long as you keep on tempo and hit enough notes to keep it recognizable most people will never notice

if you miss a note and let it throw you off than it becomes noticeable to everyone

He’s found the key notes to make the melody recognisable, like an artist can capture the essence of a face with only a few strokes