Q: have you ever tried to make a list of all the chords you could think of that could harmonize the note C or is it impractical?
A: sometimes it can be a nice exercise to put the same C in the melody and then try every bass note and then find all the best ways of filling in the harmony from there. it can be useful to know. there will never be a firm dividing line between what you can and can't do, but if you have C as the melody you'll want to know you about Ab maj, F maj, Gsus4, C over E, Dmin7, Dbmaj7, Eb6, F#min7b5 or F#dim, Amin, Amin7, Bbsus2, F/Bb, Fmin/Bb, Bbmaj9, Bbmin9, Bb9, Ab7, Ab6, Abmaj7, F over G, Bbsus2/G, Fsus4, Fsus2, F over A, Fmaj7, Fmin7, Eb13, Ebmin6, D7, D7sus4,..... that's about everything that i could come up with that seems reasonable. But any actual moment in a real song is going to render most of those wrong and a handful of them right, or possibly requiring something not listed here. On an actual songwriting situation, if you find yourself in a scenario where you'd find yourself using this type of logic to find the right chord, i find it usually means you've lost touch with the song at that particular moment. mechanics usually are not what is gonna produce the answers you want, at least in a music/song situation. for that you have to rely on pure magic/miracles, unfortunately