Limiting beliefs are exactly what they sound like - beliefs a person has that limit what they can and do achieve. The course tutor said that this is often linked to the idea that we shouldn't have what we want. This is only my opinion, but I'd guess it's probably worse in women and also when what you want goes against the "norm" of cultural values - writing rather than a high-powered career, for example.
The beliefs tell you why you shouldn't do something. No good at writing? Why bother? You'll never succeed? Why bother? Don't have time to write? Well I guess there's no point in starting, then. The problem is, when these beliefs take hold it's like a radio playing quietly in the background. They get stuck in your head like an earworm, which only reinforces them and undermines both confidence and motivation.
The tutor gave a handy and really simple exercise to help combat them. Take a piece of paper and divide it into two vertically. In the first column, write your limiting belief; in the second, write its opposite and evidence for it. Writing them down makes them real and easier to pin down, and also makes the opposite real.
Limiting belief Opposite belief
I don't have time to write. I do have time, I've spent four hours this weekend on Minecraft.
Writing is a waste of time. Writing is not a waste of time. I enjoy it, and unlike Minecraft it sometimes pays.
If another limiting belief pops up in response to the answer, write that in the first column and write its answer in the second. If you keep going long enough, you might even drill down as far as the actual problem.
As far as I can tell, this is a similar idea as is taught in Cognitive Behavioural Therapy, in that it's trying to break a destructive thought pattern. The last thing in my course notes is a reminder to celebrate successes. Although keeping outcomes in mind is important, so you know where you're going, "How will you know what you've achieved if you're always looking at the next thing?"