For Writers of Original Fiction

I usually try to be careful but it seems there is something fundamentally wrong in my brain. I suppose verbal and online messages put less emphasis on correct grammar, for better or worse, so I don't notice them on daily basis. At least, I haven't been chased by a grammar nazis on the street, as of yet.

Writing, obviously, is a different medium. I have taken grammar courses at school, after school, and even at home. I even read several grammar books for pleasure. Perhaps, pleasure is a bit far fetched.

Last year, I took a course at a continuing education program and got 90%. (This was a summer session, by the way. 40+ hours long) The mark doesn't mean much but the instructor thought I was doing alright. So I rekindled a tiny hope.

Alas, why is it that I can't seem to communicate with my readers? How bad is my grammar? Let's say it's bad enough to confuses readers and make them want to stop reading after page 2. That's on a short story with probably only few more pages to go.

If anyone had a serious issues with grammar, and overcame it, I'd like to know how you did it. Thanks.