The idea of programming something from "scratch" (whatever your definition, and programming language) is the best way to really understand something new. Reading about it, hearing someone speak about it is one thing ... but opening up a blank .c file and adopting a "ok, let's get on with this" approach is something much different.
It takes time though and one has to combat the "how come you're reinventing the wheel" comments from co-workers, spouses, bosses, etc., which can be a challenge.
This is the biggest challenge I face. As I attempt to teach myself computer science and programming, the toughest aspect is to work through SICP. I am always tempted to take the path of least resistance and follow a tutorial to build a tangible program that will impress. Must remember that this is a journey and to build brick by brick, even if that means gathering the ingredients for the clay, then mixing, then laying the bricks!
I'm not really sure it's the most effective learning paradigm. It must be easier to just copy-paste trivial programs and then try to modify them, gradually increasing complexity level, until you get certain level of understanding.
It takes time though and one has to combat the "how come you're reinventing the wheel" comments from co-workers, spouses, bosses, etc., which can be a challenge.