To be honest, I rarely become lucid through reality checks. Most of the time, I become lucid spontaneously too. I can just sort of tell by the "dream atmosphere". But there have been some times, especially when I first started, where I would RC out of nowhere during a nonlucid. That was most probably because of the habit of RCing all the time in waking life. But those seldom happen anymore.

Now, I RC after I become lucid. I think it is awareness that gets you lucid. You may not actively notice it, but you just know there's something odd about the scene. And then you get lucid. That is when I do the reality checks to make sure and double check.