Several years ago I could only play exactly from the piano sheet music in front of me. If I looked up from the music for a fraction of time I lost my place. I was only comfortable in the keys of C, F, and G. Sometimes D and Bb. But I longed to play and smile at the congregation in my church. Or check the worship leader to see if he was going to add another stanza. Then I started to learn Pachelbel Canon in D. Ever heard it? A study on the D scale. It opened my eyes to improvising or embellishing on a song at the piano.