There's probably a word I've been pronouncing wrong my whole life that I don't know about
Just based on how often I notice someone mispronounce a word without realizing it (or have done so myself and realized it later). Statistically I'm probably still doing it with some word.
One of my friends once called me pedantic, and I got to correct his pronunciation of it - he stressed the first syllable. One of the high points of my life.