For me, it has a lot to do with experience. I know what I can get from the films and developers that I use, just as I know what my various cameras and lenses will give me. When I do serious work, I think about how I want the final print to look, and I don't trip the shutter until I have that fixed in my mind (unless I am experimenting). Then, based on that final print concept, I choose what equipment, film, filter, agitation method, paper, developers, and toner(s) I will need to use in order to get where I want to be.
It doesn't always work out the way I wanted: sometimes I see things later in other images that I did not see when I exposed the negative, and sometimes I don't get what I wanted from some shots, but that is to be expected. I learn from the results I get and try to use that knowledge to make finer and finer adjustments in both my vision and my technique.
Photography is an unending learning process that cannot be rushed. I find that I learn the most when I relax and just let it come. If I try to assimilate something to soon or try to force the process, all learning stops and everything goes to hell. This usually happens when someone is trying to push some new idea on me, which is why I almost always take pictures alone. I prefer to read about all sorts of different technique and concepts and then when I get to a point that they feel right to me, that I what to learn them, then I go back and read more about the specifics and it clicks right in.
Another thing that helped me get to the point where I am is ignoring much of the equipment, film, developer, and technique banter until I had a reason to change what I was doing. I chose to use Ilford films (PanF, FP4+, and HP5+) only and use Rodinal and Perceptol as my developers because I liked the results I get with those combinations. Admittedly, I used a fair number of films and developers in the very beginning because I had no experience at all with any of them. I had shot Kodachrome for 20+ years and when I started black and white I knew absolutely nothing about different films. I chose Ilford because other people seemed to use these films often, they were locally available, and there were three speed from the same manufacturer.
As for developer, at first I chose Rodinal for one reason only, longevity. I have since tried other developers, but I find that I love the results of Rodinal and now the longevity is just icing on the cake. I chose Perceptol because I read Barry Thornton's book and thought it would be just as good a choice as any to start with and I've never had any specific reason to change so I still use it. It can be diluted or used straight for different effects and it works well.
In the end, only you can justify why you do, or don't do, any given thing. To understand what can and can't be done, on your own experience can really give you the answers you are looking for. The comments of others can be invaluable for guidance, but in the end, there is no substitute for your own personal experience...
- Randy