Not to question Brian's comments. Knowledge of your materials eliminates many problems.
However, even if you know your materials, it might be a good idea to keep making two exposures of each photograph you make. I got this idea from John Sexton at a workshop, and it makes sense to me. That second exposure makes it less likely that some mishap will destroy a photo that you really want to print. Mistakes in processing, a dumb mistake while exposing the film, dust spots in the sky, and many other problems can be remedied if you have that second sheet held "in your back pocket." I have experienced this firsthand. I dropped a wet sheet of film on the floor, then stepped on it (duh!), scratching it in the process. I was happy to have the second sheet.
Just a thought.