In a dream, a person often isn't aware of what events preceded the events currently taking place in the dream, right? That's because there ARE no events preceding the dream. If a person starts thinking to themself "how did I get to this moment?", they'll realize that the moment came out of nowhere, and then they'll realize that they're dreaming.

So, if you make a habit of constantly asking yourself "how did I get to this moment?" in real life, that habit will transfer to your dreams, and result in you attaining lucidity on a regular basis.