I think a lot of the "confidence" is taken essentially philosophically too. A lot of people who are willing to work on the prosecution side firmly believe in some type of "procedural justice", the notion that a verdict reached by properly following all legal processes, even if factually incorrect, is a just verdict. There's a big "assuming the process is fair" part of that belief, but those people don't go in thinking the process is unfair, and then also contributing to the process being unfair.