Well, at least for me. When I was an art student, I used to have this issue when I was drawing. I would start a picture and fall in love with a way a section was turning out. Instead of looking at the whole picture, I would just keep working the area that I loved.
I do the same thing with my workouts. I'm still focusing on my upper body. I did an hour upper body workout with Maya today. It was a gruelling workout. I think part of the reason I like her upper body workout so much is that it's actually a full body workout. She has me do a lot of lunges/squats with some upper body moves (like shoulder presses). She also always ends with a core program (someone really needs to tell her that if I can't do straight leg planks, there's no way in hell I can do one leg planks). So between a good 20+ minutes of cardio, then all those squat/lunge combos, back, shoulders, bicep and tricep exercises, I also get some nice planks (plus all those chest presses/flys on the ball will work my abs too). All in all the hour workout burned almost 400 calories. Maybe that's why I like the upper body workout so much.
It also may have to do with the missing fat pad on my back. That was one of the triggers for me to start losing weight. I was getting a fat/hump between my shoulders. It was making my posture worse (I do not have good postures). It's completely gone. I also have better posture.
However, I still have so much to go. My upper arms are still heavy. The muscles are there. I've been surprised at how much muscle I've been able to develop, but I still have too much fat on my body. I'm working on it, tho. I'm back to a 1500-1600 calories a day diet. My current goal is to break the 150lb mark.