Me too and I think homonyms are partially to blame because spellcheck never catches them. Also, my first grade teacher wasn't so good in teaching spelling. I remember if you got a 100% on your weekly spelling bee, the teachers would adhere a cutout apple with your name on it onto a big cutout tree. I clearly recall walking by the other 1st grade classrooms and their spelling trees were loaded with apples, while my class's tree was not.

Another reason is we spell words like they sound which is great if you're Italian because apparently all their words are spelt like they sound. However, English has a lot of words that you can't figure out how to spell by simply "sounding them out" (As my teachers used to always say). It took me ages to figure out how to spell viola and bidet and diarrhea. You can't sound them out! And while we are on the subject, there should be an onomatopoetical word for diarrhea, something like "splatch".

BTW, I had to Google the spelling of "onomatopoetical", now if I can only remember how to spell it :).