I think I have learned it almost once a year starting with freshman year of high school in Biology - and then again in AP Biology senior year, and then in both Intro to Biology and Intro to Chemistry in college, probably in Physics, again for the MCATs, again in Biochem in med school, definitely again in Physiology, again to teach the MCATs, and now again in Pathology.
I think I actually understood it for real for the first time last year in Biochemistry. The seventh time's the charm, that's what they* say!
Even though I get it now, pKa still gives me nightmares sometimes.
*by they, I mean me, when it takes me seven times to learn something