Okay, so I found out about lucid dreaming about 2 weeks ago and introduced it to my roommate about 3 days ago. One day he told me he had a dream about a friend 2 years ago. They were hanging out at the friend's house and his brother, playing the Xbox and whatnot. Now here's the kicker. His friend is an only child in real life, but while dreaming, he easily accepts it as it's completely normal. After waking up, of course, he realizes that his dream makes no sense.

Why is it that he can't realize this in the dream? And what can he do to realize this if a similar case were to happen?