If it's true that how you think and talk to yourself determines what you can do, then my trainer Amy is my oracle.
I had a great session in the gym yesterday with her, working on both upper and lower body core. If you've never worked with a trainer, then it may be hard to picture what 30 minutes of intensive focus can involve. She has me working on machines with various amounts of weight to work certain large muscles...as well as exercises done with props to center my balance and to extend my range on big muscles I use to walk. She also has me doing mat work that more falls into the pilates/stretching arena. And she's more recently added push-ups as well.
Amy is careful not to praise me inordinately -- she knows I have a good ear for bullshit, and a fair sense of my own progress. So her comment yesterday meant a lot. That's not the end of things, though. She will continue to push me.
Everyone should have an Amy.