The concept of a "second brain" is jotting down things in various apps so that your "primary brain" doesn't have to "remember" them, and can thus focus on more creative activities. But I think the idea is fundamentally flawed.
Apps are bad "second brains" because they don't think. Moreover, excellence is not achieved by merely "remembering more."
When we master programming, we don't carry binders that we keep referring to. We internalise concepts and apply it to novel situations at will. Merely dumping text somewhere is not a replacement for thinking.
Sure, record-keeping has its purpose. However, a record is only as valuable as it can be interpreted, and it's the person doing the interpreting who is doing the "thinking."