Illiteracy used to mean not being able to read and write. No longer. As Alvin Toffler says above, it means much more. Its definition has broadened while also becoming much less specific.
Over 30 years ago, my father-in-law decided to retire. He had worked for more than 30 years as a draftsman and loved his work. He enjoyed the precision and creativity that his job allowed. Throughout his time as a draftsman, he moved from pencil and paper to learning to do his drawings using a computer program. As T-squares, pencils and papers were moved further and further away from his work life, his desire to retire became stronger and stronger. He finally made the decision to retire and never looked back. When asked how he knew it was time to retire, he said quite clearly, “I didn’t want to learn another way to do my job. I loved my work, but I didn’t want to learn anything new.” In other words, he didn’t want to unlearn and relearn. For him the timing lined up. He was old enough to retire and had a good life ahead of him with lots to look forward to. For others, things don’t line up quite as nicely.
In education – as in most other fields – learning, unlearning and relearning are constant states of being. Many times the barrier is one of mindset rather than difficulty with the skill or concept. It’s one thing to decide at retirement age that you’ve learned enough and it’s time to move on; that’s not so easy for most of your work and school life. How literate are you? What have you unlearned and learning recently?
Everyone I know considers him or herself to be an intelligent person. We all like to think we know things and are able to carry on a dialogue that is informative and demonstrates our abilities. On the other hand, many people I know are quite uncomfortable with change. When the unexpected occurs or things do not go as planned, it can be challenging to adapt to the new circumstances. 
The dust has settled; the children have finished another school year; the sixth-graders have graduated and are moving on to middle school. As we performed all of the tasks necessary to make graduation day and the last day of school meaningful celebrations that everyone will remember with fondness, we also are thinking of next year and all that it promises.
The Montessori Message 