This is definitely true. I find when you 'know' you're going to have a lucid dream that night rather than think/hope you will, you almost always do.

Also I rememeber when I was first strating out and wasn't so confident in my ability somehting that really helped was using the NLP timeline technique (I think it goes by a few other different names too). Using this in place of a normal affirmations / mantra really sped up my progress in having more regular lucid dreams.

Timeline technique:
Basically if you visulaize your life on a timeline with your past extending out in one direction, usually either off to your left or behind you, and your future off in the other direction. Then you can imagine floating up out of your 'present body' and moving along over the future part of youu timeline untill you get to some point where you see yourself as regularly having lucid dreams and are very confident in your ability to induce them on demand. Then you drop in to this 'future you' and take a couple of minutes to really feel how this future version of yourself does; What does this person feel like being able to have lucid dreams on demand, how do they talk about it, what is thier body languag elike etc. You can then return to the present version of yourself whilst holding on to this feeling.

Even if you don't start off feeling that confident your mind is easily able to imagine what it would be like to feel like that when given a chance, and once you are feeling like that it still has the same effect on your ability to induce LDs - it doens't really matter that you just imagined that feeling of confidence into being!

Hope thats helpful.

Also I was just wondering if anyone else ever tried something similar? How did it work out for you?