RE: When Do You Stop Believing?
Not that I ever had many such mishaps with kits, but I always try to read the instructions completely at least once before I begin to build. Then when I build, I always keep reading a couple steps in advance, sometimes it answers questions before they come to mind. In any cases it helps understanding where I'm going.
I'd say that if that + reading the plan would not answer my questions, I would, in line with the next steps in the build, begin to modify. But only just enough to be able to continue with the manual.
Ciao!