For me common spelling mistakes include confusing some of these word pairs.
- loose vs. lose
- then vs. than
- were vs. where
2·11 days ago- centennial, millennial, embarrassed, etc. (Where are the double-letters and where are they not? Who fucking knows.)
- backward(s), forward(s), leftward(s), etc. (Do words like this have an S or not? Who fucking knows.)
- reconnaissance (Just fuck this word.)