To live in the present—an advice we have heard of many times to reach long lasting happiness.
Past memory is banished because it invites stress from dwelling over our life tragedies. Future thought is forbidden because it leads to worrying about undesirable outcome.
But we need past memory to establish our identity, to reconcile our experience, to learn from our mistakes. We need thoughts about future to ensure we still have food to eat, to plan for accomplishing our goals, to set hopes on our children.
If living in the present moment grants lasting happiness, amnesia patients would be experiencing long-lived felicity.