I must say that there are also errors and wrong notes and/or chords in written music. You don't notice too much unless you are playing both melody and accompaniment. You play it as is writ and your ear says 'bugger off, that just ain't right!' so you adjust either the chord or the note so it is no longer discordant. There is also the question of your brain saying 'bugger off, that is too complicated' and coming up with a routine that fits perfectly but the old hands can cope with :-)

DtG