Problem with Mantras?

Hello!

I usually use mantras before falling asleep or after performing WBTB. I will first say a few times aloud and then mentally repeat till I fell asleep.

When I use some of the type: "I remember my dreams", "Wake me at a specific time", these mantras always work correctly under normal conditions and with a success rate close to 100%!!!

But if the mantra is like: "Tonight I have a lucid dream", "When I'm dreaming I realize I'm in a dream", NEVER works!!!

Can anyone give me an idea of ​​why?