In school I was lucky enough to have lots of English teachers that encouraged creative writing. We wrote short stories, poems, memoir in many different grades (and thus with many different levels of quality) but I didn't have many teachers that taught us much about mechanics. I was on the cusp of the 'free writing' movement, by the time my brother hit middle school grammar rules had been thrown out the window and the feeling and intention was paramount. My teachers weren't that nutty, but there wasn't a big focus on where that comma should go.
I'll admit, that followed me. Sometimes commas feel like a mystery. I recall specifically my senior English teacher giving me a mini less on the back of an essay about semi-colons to get me to quit it with the run-on sentences. I love run-on sentences. In middle school I did have one teacher who would know 50 points (of 100) off our grade for a single offense. Luckily she split grade content/grammar. I got a lot of A/F's in her class. Obviously it didn't help because senior year I was just discovering the semi-colon. A lifesaver eventually. Thank god for Ms. Crago.
I realized that my big problem with those run on sentences was Latin class. I took six years of it, and let me tell you, those Romans liked a long sentence, and a comma (well they didn't have commas, but when you translated it, you used them). So Latin class was my grammar foundation. Id translate four lines and have just one sentence, and there it was correct. Back in English—not so much.
So, dear readers, if you find an extra comma that has escaped my edits; sorry, but blame the Romans.