It doesn’t take much to please her: A walk, a kiss, a smile, some dinner.
But the moment you set an expectation, she expects it not only to be met, but far exceeded.
You told her you can play the piano? You better be good at it. You told her she would like it? She better love it. You told her you would take care of it? It better be done already.
If you mentioned it, it’s because it was worth mentioning more than anything else.