How can one “leave the past in the past”? The past is not a bag that one can throw to the ground and walk away. Neither it’s hair which can be cut off. The past can be left in the past only if you find a use for it. It’s like oil that came out of the ground in the garden: bad for the harvest, but you can derive a benefit. The same with the past: it must be disposed intelligently, rather than thrown away.