I never understood my DS's cries. I remember when he was little reading about different cries, I read books, info on-line and all sorts thinking it must be possible to work this thing out but for me it just wasn't possible.
It was the routine which led me to know what he needed. To the outside world I looked like I understood his cries and there are some spectacular stories about "understanding his cries" and knowing just what he needed and being able to sooth him in seconds, but actually the reason I knew was the routine.
Separately from the routine there were times when he cried and I just didn't know what was wrong or what to do. There was more than once when I told him I was going to leave the room (him in his cot) to see if that's what he wanted and that if he continued to cry I would come back because it turned out that sometimes he was crying "go away and let me sleep" which was hard for me to accept because in my head I thought he had to be happy/soothed/calm before I left him and that I could not leave my baby crying. Several times it turned out he did just want me to go and would nod off the moment I was out the room, other times he didn't so I'd just go back in.
The EASY routine made me look like I had more understanding and instinct than I really had...and then over time I really got to know him much more and it became easier for me. Easier still when he could talk and say "you can go now" oh, right, thanks, okay