I will admit, my first couple of long works, I was so obviously the main character. But I was learning the craft, and those stories will never see public consumption (unless I die a famous author and my kids sell them for money, but I'll be dead then and won't care). When in the early stages, sometimes it helps to put yourself in because you know the character. But, even then, the self-insert characters should not be perfect In my case, they made many mistakes, and (in one of them) was not even the main character, just the MC's best friend. I don't think they were Marty Stu characters, at any rate...