tkamiya, this happens to me often, usually when I put myself in the darkroom for long periods of time, or night after night after night. It gets draining and seems monotonous. I have worked hard a few nights in a row to make a print, only to not be satisfied with it. But I will keep the prints and I store them away. I have dug up the same prints a month or even a year later and said "OMG this is an awesome print!" I think that maybe staring and working with one image for too long becomes draining. But it's hard for me to move on to another negative if the current negative I'm working on is dust free and already in the carrier and focused.
Guillaume's point about variables changing between printing sessions is very true. Making a series of prints that have to be absolutely identical should ideally be done in the same session. Things like body heat heating up the air and then the developer just a little bit, or an enlarger bulb losing intensity, or even the age of the paper you're using can have an affect on the prints you're producing, and if you wait days or weeks or more between printing the same negative any of these factors and other may have an affect on your results. I prefer to get the final image in one or two sessions at most. When I get there I make 2 or 3 more identical prints, then if I have time tone them, if not that can be done at a later session.
Some things to think about before going in the darkroom to print. Contact sheets are absolutely priceless to the printer. I make all my contact sheets at grade 2. Some make them at even lower grade. I also scan all worthy frames and save them on the computer. The frames that have the most potential go into PS and I mess with them. Lighten, darken, dodge, burn, even simulate different tonings. I find this process absolutely priceless to me as well as I can already see how I want my print to look before the negative is even in the carrier. At this point I go back to the contact sheet and stare at it, then stare at the "simulated" final image on the computer screen and I go back and forth predicting exactly how I am going to print the image, what grades I will probably need to use, whether I need to split grade print it or not, and where to dodge and burn and most likely with which grade. And since I already figured out which toning I prefer best in the computer I can predict for the contrast increasing effects of selenium toning, or the need to print slightly darker in the highlights if sepia toning warmtone paper. This is my workflow and I wouldn't have it any other way. I can enjoy the scanned images in the meantime on the computer and after a month or more may decide the image is not worth going into the darkroom with. If I didn't have the ability to scan and play in PS first I'm not sure I'd be as good of a printer as I am.. well maybe, but I wouldn't have a clear vision going into the darkroom, and this could be viewed as being a bad thing or a fun thing. Regardless if you scan or not, you need to focus on your contact sheets and try to visualize which grade or grades you may need and also where you're important highlight and shadows are to begin to make test strips, and where burning and dodging may need to be done. Best you can do is be consistent not only in your printing workflow but also shooting workflow as others have mentioned. If you're feeling overwhelmed at all with the process or feel like you wanna give up it's definatly time to take a step back for a day or more and regather your thoughts.
Here are a few threads I started which are similar to this one you or others may find interesting:
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