I once heard a supervisor tell an apprentice, “I’ve forgotten more than you’ve learned.” That’s a pretty arrogant and offensive comment to make to a learner. But there is a bit of value in it.
I’ve always maintained that there are two aspects to learning, the acquisition of knowledge and the development of skills.
Knowledge is important. You can’t really develop skills if you don’t know what you are trying to learn. But it is also important to remember what you learned. It’s not just information that you need to pass a test, after which you can just forget it.
Skills also need to be maintained. It is said that one never forgets how to ride a bicycle. But you can get rusty if you don’t practice a skill. Your hands forget how that sweet plane cut feels or how to maintain the correct angle when making a saw cut.
We have to remember the knowledge and continue to practice the skills or the learning process can reverse itself.