You know you are *really* learning English when…
…you start writing “two” instead of “too". I’ve been making that kind of silly mistake more often lately.
I learned English mostly by reading and writing, so I suspect that I thought of words as sequences of letters. Since “two” and “too” are different sequences with different meanings, I could never confuse them. But they sound the same, so now, after speaking English for a few years, I must be thinking of words a bit more phonetically, because I’m starting to make some of the strange mistakes that the native speakers make.
I just hope that I never write “principle” when I mean “principal", because if that happens, I’ll eat my hat!