One of the frustrating things with analog photography (and actually one of the redeeming qualities too when it works) is that you can't check the back of the screen to see if your exposure is spot on. I find that a good thing often because that makes me focus on the picture taking and being careful with the exposure to begin with, because I can't check it after each image.
Usually that is...
...however, when it goes pear shaped it definitely can do so in a big way. A few weekends ago I was in Copenhagen, Denmark to shoot the Japanese culture festival, a.k.a. the Sakura Festival and boy did I mess up the exposures a lot! Especially the shots I did with the Zeiss Ikon Nettar medium format camera turned out a complete disaster. In hindsight I know now that I can't use the same exposure values for a sunny day in April as I'd used on a cloudy day in March. While the camera isn't perfect by a long shot it can certainly expose at a smaller aperture and shorter time when the lighting is good. I should have remembered that. A lesson learned for the next roll!
Also, it's not a good thing to get light onto the film at any point during the process, because then you can end up with ghosting effects of the perforations as I did with some of the 35 mm shots I also took that day. I think I accidentally did that when I had to adjust the developing tank lid halfway through the process. I thought I was careful enough by turning off the light and covering the tank with a towel, yet somehow some stray photons of light managed to find their way in there. Frustrating, but at least that's a mistake I won't do again!
I've tinkered with the shots in Lightroom to correct my exposure mistakes on the 120 film and crop out the light leaks of the 35 mm shots to a large extent, and they're at least tolerable now.
Below are a few of the shots I did with my Canon TLb 35 mm camera that day. They were from the first bulk loaded roll of Fomapan 400 that I purchased a few weeks ago and I hope I do a better job with the next rolls, because I wasn't at all satisfied with the outcome. However, this was most certainly more due to the photographer's incompetence than any shortcomings of the film!