Confidence is harder to come by than winning lotto tickets when you don't have enough of it.

That is SO true.

Personally it seems like those assertions create their own resistance which stops them from working (assertions imply worry, worry implies doubt, and it's an ugly spiral down from there).

That's the same problem I keep running into. All I can figure is that I have to resist the resistance, and persevere, if I am going to get over it. I can't skip this part, I have to fight through it. If I can't convince myself, no one can do it for me. At least that's the popular theory.