Your memory is a monster; you forget - it doesn't. It simply files things away. It keeps things for you, or hides things from you - and summons them to your recall with a will of its own. You think you have a memory; but it has you!
Mortality means you don't have forever to work things out. You can live your life unexamined but then on the last day you're going to think: 'I've left things a little late.'