Rolling was a huge mountain for me when I first started. I'd be so afraid and tense up which made it alot worse, for the rest of the lesson but especially for my headspace the next time. Most of my shoulder would be bruised and sore to move between classes, I don't think I could have stayed if the people weren't so lovely and supportive.
Towards the end of 4 months I fluked a roll a couple times and something felt right, I started getting the feel of what it was supposed to be like. It gradually dawned on me that maybe my focus was off. Each time I tensed I would fall straight downward while I tried to roll. It was like the only thing I wanted was to be able to fly gracefully like the people in hakama during demonstrations.
I decided to change the picture in my head, I started visualizing a seagull skimming the surface of the ocean as it flew. I imagined that the expanse of mat was the water and walls didn't exist. Momentum from other people throwing me helped me fly too. Eventually I started thinking 'out' rather than 'go down into a roll', and it worked! Beating gravity's brilliant fun!
Learning to roll was hell, but that's what makes it so much better now.