Why is it so hard to astal project? I had done it one time, while half heartedly trying....but now nothing!?

Over a year ago, I had been trying to move my 'astral body' for a few nights before going to sleep, and the third night when I didn't practice, I woke up as I was leaving my body. I didn't expect that to happen, and it startled me so much I panicked and grabbed onto my husbands arm and woke up in my body. Now that I try to do it, so far I've had no success. I've read books that Robert Peterson and Monroe wrote, and keep trying. I wonder if I'm trying too hard...