Lately I've been trying to learn one new thing every day. And one of the sad discoveries that I've made is that I'm capable of forgetting things almost as quickly as I learn them.
So, two months after I learned how to write vim macros - I've already forgotten the specific keys used to define and run them. Now, I can re-learn this very quickly - I've got good notes, the memories are just slightly hidden, and I haven't forgotten any concepts, just simple keys. But this will slow down my use enough that I probably won't pull this tool out when I need it.
This got me thinking about how I needed to complement training with some some repetition, some practice. That just learning something isn't good enough. This is exactly what martial artists do - they would call these katas. It's also what musicians do - they would call these scales.