Pick up the wrapper even if it’s not yours. Nobody’s watching, and that’s exactly the point.

Small unwitnessed acts have no incentive attached, and that is the whole substance of them. Nobody thanks you, nobody sees, nothing improves for you personally. What actually happens is that the place is slightly better and you are slightly more the kind of person who fixes things instead of stepping over them. That second part accumulates faster than you would think.

Pick up the next piece of litter you walk past, even the one that is clearly somebody else’s. Push the trolley back, straighten the chair, close the gate. Five seconds each, and they add up into a habit.