Well, I often do feel that way. I'm sure most writers feel insecure to some extent, even the famous ones. In today's day and age, the audience for writing is in fact shrinking. We have to keep plugging away anyway. Right now, I'm on this site trying to read people's stuff, hoping that if I comment on theirs, they will hopefully read mine.
Bob is of course right, that if you don't think your stuff is good, then others won't as well. However, I think most writers have a fraught relationship to their work, enthusiastic one minute, insecure the next. I think Bob is right that, if you are working on a particular piece, and it isn't exciting you, you should abandon it. However, you shouldn't take insecurity as a reason to give up altogether. Focus on what you do well, and just get out there and share it with the world.
"Success" will only come to a few of us, but as we are working, others are giving up. In the end, if you can survive and do what you love, then it doesn't matter who pays attention.