This is a long error that has run with me, so it is better to have to an understanding of why, I always used I in small letters, whereas I am always corrected that it is a capital I e.g
I am not feeling well, so I might take a day off to see the doctor and I will let you know. is right
I am not feeling well, so i might take a day off to see the doctor and I will let you know. is wrong
The way I understand English is, we don't use capital words in between unless followed by full stop. e.g
I am tired. I must take rest for five minutes
My understanding of English grammar is, that everything is small letter until followed after a full stop, so why I different?