It ain’t impossible. For starters, you may want to adjust your definition of the phrase.
As cool as it is, the most common interpretation of it just isn’t going to work (for most of us), unless you count controlling your own body as well. Instead, loosen the meaning of “matter” a bit. Yes, we’ll be staying within the confines of our own physical body, but I won’t make any more jokes about making your arm move being a psychic ability.
Do you know how, if you have enough willpower, you can run an extra half mile after your legs have already started feeling really sore? Or how in dire situations, people are capable of very impressive physical feats they otherwise wouldn’t have dreamt of achieving? That’s mind over matter. Not giving in to the feelings of weakness emerging from your body, not letting your mind be swayed by the desire to stop and take a break, that’s mind over matter, right there.
We aren’t psychics, but we’re certainly masters of our own physique. And that’s really worth something. Use this great power wisely.