Don't ever forget what u've learned before, as u may come across to the same situation, where u need to apply the things that u learned.
Sometimes we tend to think that, "I know how to do this, it's simple", but when we really have to do it on our own, we get nervous, and the things that we thought we "know" will be suddenly missing from our head. In the end, nothing comes out.
Sometimes after someone taught us on how to operate a machine for example, keep the information in mind and never forget it because as we get to the higher level of practice yet we don't even know how to operate a simple machine, guess what...HUMILIATION is waiting for U....!