Get Back to Ballet.
(A couple months back I - temporarily - started waking up with the New York City Ballet Workout and the changes were instantaneous. Tight core! Great posture! The ability to bend! These changes were so exciting that I rewarded my hard work with a couple days off, which stretched into about three months of pure relaxation and pure stiffness).
Chances of seeing this through: 42% (for two weeks straight).
(That's me at age 5, a time when I was exceptionally bendy. My mom and aunt thought I was being exceptionally dramatic when I complained about the crunching noise and the pain in my wrist after doing a back walkover in my backyard. But they reluctantly took me to the doctor. The x-rays came back. Mom took one look, saw nothing jutting astray, and chided me for this waste of time. The doctor came back, pointed out the break and stuck me in a cast for the next six weeks).