1 out of 10 to 20 messes up for me, and that is usually because I use a lot of oily wood. I know to expect that. Don't expect instant perfection. CA is not easy for most people. It is a great finish but it takes practice and learning how to incorporate personal style, sandpaper likes, pressure and speed. For some people they seem to be insulted at the CA when it doesn't work for them. For me, it took about a year and a half of - off and on pen making to get the "feel". I did a few great pens early on and knew that I liked CA as opposed to other finishes. This drove me to continue until I had the feel and could predict which CA was needed with which wood.
I don't think most people will take as long as I did, but I was driven to learn it (when I had time) and it has finally paid off.