How should I think if my mantras while falling asleep fail?

Let's say I repeat the classic mantra "tonight I will recognize that I am dreaming" over and over until I fall asleep, and I really believe in it;
what should I think of this method if that mantra doesn't succeed that night, or several nights after that?
This is one of my stumbling blocks right now - if I repeat something for several nights and it doesn't succeed until a couple weeks or whatever, how should I treat this in the meantime to keep believing in it?
I am wondering because I think it's a bit discouraging when something you have chosen to believe in doesn't succeed immediately, because that kind of seems to make it harder to believe in it next time.

I was going to try out the mantra I mentioned tonight, but if I don't recognize I am dreaming it feels like it will be harder to believe in it the next night.

Mantras or any kind of induction method may take a while to work. Patience really pays off. The thing to avoid is thinking "this isn't working" or "I can't have an ld for n days now".

Your subconscious is like a small child, it will believe whatever you tell it, which is why you have to be positive about the outcomes of your practice. Autosuggestion whether positive or negative can have a great impact on your subcon and the result. Be confident! You've done it before and can do it again! :)

Though NyxCC's advice is key, here's another thought:

Never make your mantra in the future tense. Saying "Tonight I will recognize that I am dreaming" will allow your unconscious to place your lucidity into the future, and thus keep it out of your current dream. It may sound silly, but keep it in the present tense.

Also, instead of using a "classic" mantra, why not use one that carries more meaning to you, and your goals? Meaning is everything in the mantra department.

Plus, it might help to use a few less words in your mantra, so it is easier to repeat and carries simple clarity (ie, "Tonight I will recognize that I am dreaming" might work better as "I am dreaming."

Okay, that was more than one thought...

One fundamental thing about LDing is believing that what you are doing will be successful. Because Lucid Dreaming is all in your head, any doubt will RUIN you.
It is very important to honestly have faith that your mantras will work. Also practice them in daily life.
For example: my mantra is, "I notice details and become lucid/aware." I practice this with SAT (Puffin's DILD Guide - Lucid Dreaming - Dream Views) while inspecting the details of my surroundings and how I feel while repeating my mantra. I also repeat it before bed.
I outline a bit about mantras here as well:
http://www.dreamviews.com/attaining-...technique.html

Good luck!