Can you really change someone?

Can people be changed? There's a saying that comes to mind when I think of this, 'can a leopard change its spots?' That saying seems to imply that you can't. I think it's difficult for people to change but it is possible, it probably takes a great effort, no a herculean effort, for most people because people tend to be set in their ways. That's talking about big changes, a big shift in the paradigm of thinking. There are little things that can change over time too, small habits that we can discard or acquire. But ultimately, I think we tend to stay true to ourselves and our core values which are set during childhood. If that's the case then trying to change someone in a relationship is going to be hell and probably could be the cause of many a failure. But if people are willing to compromise, if that's part of their internal makeup, to adapt and willing to change, then they will be the ones who will have a better chance to survive, whether in a relationship, or in work, or in life.