It means accepting that your knowledge of old subjects will decline and that there will be a period of hard effort before they're usable at their previous level.

We are all apt to forget things we have learned in the past. Even memories of important events will eventually decline in accuracy.

A strategy to adopt is to embrace relearning opportunities. It may mean there's a chance you'll fail, but adopting a policy of embracing opportunities will lead to better skills in the long-run.

Relearning is an excellent strategy for lifelong learning. The problem is the pain of rebuilding confidence. You may remember a better ability than in reality, so even doing your best with the old skill will seem sub-standard.