In a world of karma and causality, "Changing the past" is the only thing worth striving for.
You are trapped, inexorably, on a rail-path that pulls you into the future that the past created.
You cannot make anything in the future 'better' without in some way changing the past.
The Trying-To-Be-Wise say, "You shouldn't try to change the past; you should try to accept it."
What do you think changing the past feels like, from the inside?
Once the past has truly changed, you don't *feel* it as changed; you feel it as has-always-been.
"Failure to accept the past" is merely the experience, from-the-inside, of what it means to need to change the past.
"Accepting the past" is merely the experience, from-the-inside, of having changed the past so that a better future can happen.