Alternate thought for "I’ve tried before and failed."

Hello! I’m working on my homework for March. My intentional sentence is “It is possible that I’m capable of losing this weight.” But, I’m having the conflicting thought “This won’t be any different than the last time you tried in Scholars to lose weight. It didn’t work then (and I worked really hard!) so it can’t possibly work now.” How do I argue that? I can try to maintain faith that maybe this time will be different…but by that same logic, maybe it won’t.