I have no problem with 'fake it till you make it.' Seriously. It's been an excellent technique for everything from prepping for job interviews, to dating, to seducing, to managing my employees, to LOA, and overcoming debilitating shyness, speaking in public, dealing with relatives, meeting and conversing with strangers comfortably.
You just have to be sane, first of all. Not everyone is, actually. If you aren't, this may not be the technique for you.
Telling yourself something that isn't yet true is a tool to help you get in the feeling place and mindset of what it will be like when you ARE that thing, whatever it may be. It's not a lie. 'Belief' that it is true is the overrated aspect of this. You don't have to believe it's true, only that it will be.
It's not a lie, it's a trick. Not a mean trick; a useful trick. The subconscious mind literally believes everything the conscious mind tells it. The more it hears it, the faster it tunes in with that reality. It has no inherent ability to discern between real and fake. It has no protection from the conscious mind run amok. Which is why physically normal people can be mentally ill.
You aren't fooling yourself. You are retraining your subconscious mind when you do affirmations. Filling in the deep ruts of dysfunction with fresh, alternative ideas. Energizing the subconscious to reflect upon these new paradigms instead of listening to the same old recordings it normally plays over and over.
My favorite and most powerful affirmation along these lines is: When I am feeling unwell, weak, tired, worn-down, or in pain....I say to myself "I am young, healthy and vibrant. I have the energy of ten strong people. I can seemingly go for hours.." or a variant of that basic theme. It's like energy just flows from my brain to my body. Aches and pains vanish instantly. I almost tingle with power. Once I realized how easy it is to change state simply by using power words, I use it on myself for all kinds of issues.
Another technique I use that I have never heard of before is: When you have passive moments, do a little game with yourself like Success A-Z. Choose a word that means something successful to you that starts with A, then B and so on. I also do it for health-related terms. Some of the letters are quite difficult but you can make stuff up like "Zing!" for Z. I find it keeps my mind on good ideas and off of bad ones. When I was in the darkroom on and off every few minutes, it was a great game.