Lucidity can happen at random. I haven't had many lucid dreams (2 lol) but I do know that you can spend a whole dream talking or reading about lucidity and never get the point! I just had a dream like that. I was talking to my sister about lucidity, and never got the idea to do a reality check.

It can be triggered by the subconscious mind, which is why I think it happens at random. The first time I had a lucid dream, was just because I had been thinking about it a lot. I became suddenly interested in it, so I had one. The other time I had been doing the hand reality check, and I did it in a dream. For most of the people here, I'd say since we practice techniques for lucid dreaming, that probably has a bit to do with it, eh? but it's largely just what you think about and how aware you are during the day.

-Rain