Acceptance vs resignation

Hi there, I am a diamond in scholars. I’d like to ask you a clarification between the difference among acceptance and resignation. When I am confronted with circumstances that I judge as negative and which I know I have no agency to change (I gained fat in the past and now I’ll always have loose skin, which can can get more and more saggy, while cannot go away), I try to play with some intentional thoughts (‘This has happened’) to go to neutrality but I see my brain shifting to resignation rather than acceptance. The very same thought ‘This has happened’ can bring me for some circumstances to acceptance for other to resignation. Could you help me clarify why that happens and suggest some thoughts to play with? Thanks