I'd always vaguely wanted to fly, but "knew" I couldn't afford it.
Then one day someone organised some trial lessons for a gang of mates, and I went along. "How much does it cost to learn to fly then", I asked, and on discovering that I had more than that sitting around in the bank doing nothing, I started learning within a couple of weeks.
So that was basically down to a fixed mind set (I forget the "correct" term, it's in the HF book) that I knew I couldn't afford it, because I couldn't when I was 20, and had failed to re-check this assumption during the following 15 years.