In the Beatle song Yesterday, Paul asks so many things about the past that doesn't give us any answer. What has been done cannot be undone either practically or via a time machine. The future is yet to come. So, we are left with the present moment where there are a lot of things at our disposal that can be changed. Change is not about yesterday or tomorrow. It's about what can do today that can undo a lot of mistakes in the past and pave the way for a better future.