“First, to be useful, learning requires memory, so what we’ve learned is still there later when we need it. Second, we need to keep learning and remembering all our lives. We can’t advance through middle school without some mastery of language arts, math, science, and social studies. Getting ahead at work takes mastery of job skills and difficult colleagues. In retirement, we pick up new interests. In our dotage, we move into simpler housing while we’re still able to adapt.”