'Thank you power' is writing down the moments that are good in your life so that you can go back and reflect on them - so you've got this sort of repository of good stuff in your past.
I sensed that my life was better when I focused on things that were working as opposed to focusing on the long list that goes wrong, but I wanted to know if there was any validity to that.
What I've learned is there's a scientifically proven phenomenon that's attached to gratitude, and that if you consciously take note of what is good in your life, quantifiable benefits happen.