I don't think it has been coincidence, but I'm pretty sure every conviction about things you're able to do are either Placebo or Nocebo. So I think this is the reason.

I didn't try it out that way, but I used self hypnosis with affirmations, which were pretty close to your mantra. They worked very good for me and I'm still impressed by their power. Actually I'm even convinced, that everything within our mind is changeable.