Not all change is hard. If I decide to change my shirt, the change can happen immediately - just find a shirt I like, pay some money, and put it on.
But sometimes change is hard. If I decide to get in shape, that decision alone won't change me. I need to consistently do the right things over an extended period of time before the change sticks - which means that I need to make a lot of right decisions everyday for a long time.
So when change requires that we consistently do the right thing for a long period of time, then it becomes hard - especially if it entails overcoming old habits.