Programming Cone of Experience

The Cone of Experience is a model formulated by the educationist Edgar Dale in which he summarized the various learning media and their effectiveness. Like every model, it has limits and should be adapted to your personal vision, but since learning is something a good developer does every day to improve himself, having a methodology for acquiring new knowledge is fairly essential.

The Cone shows different activities in crescent order of memory retention. People are generally able to remember more things if they are learning trough the lower and larger layers and less if they are working in one of the top and thin ones. We will show an example of a developer learning Test-Driven Development and good software design, comparing different layers of the cone. There are many examples of phrases like "People remember 10% of what they read, 20% of what they see, ... 90% of what they do", but these numbers are totally made up and there are no quantifications in Dale's original work.
However, this is the Cone:

Let's analyze the different way a developer can learn a new technology or practice, such as TDD. We will start from the less powerful experiences and descend towards the end of the cone where the experiences have a great effect on the human memory and we are less prone to forget and confuse informations.
I want to learn TDD, so what I can do?

• I read a book. However, reading one, two or ten books does not make me an expert on TDD or software design, and if I don't refresh my knowledge often I will probably forget everything but Red-Green-Refactor.
  
• If the book has nice figures, they will improve my understanding and I will be able to remember at a glance different concepts that fit together in a single picture.
• I listen to a podcast or see a video of Misko Hevery doing a talk at Google. This is more impressive for the brain and typically will have a longer-lasting effect on me than reading a book.
• If I see him writing code in real time, the experience is even best.
• The next step is simulating a real world situation by writing code for a toy project. This is also probably the last step we can make.
  
• The final step is real experience: TDD some classes for my preferred application and analyze the results, then start again. The real experience is often not available for learning, or it presents some restrictions, fortunately: think of surgeon that practices on human beings. He must gather real world experience, but he is under the strict control of senior colleagues for years.

So suppose you want to learn TDD or the new technology. What you should do? Skim a book of course, to know the theory. But don't stop here: write code snippets, compile real code, work on a small project you can afford to throw away. If you have the time and the money to invest, go to a conference where in one hour the speaker will give you a general knowledge of the subject.
If is it available, a live coding session is the best thing to start with a new technology or language. That's why in university's exercise sessions and laboratories we learn much more what we would do while staring at a professor. Taking notes is a step further down in the Cone of Experience, but if you are missing pieces because you are too busy writing down everything to bother listening to the professor, it is not an improvement.

The hello world applications presented by many frameworks are not meant for being simply read. They are made for being compiled and hacked. The usefulness of a hello world program resides in helping you setting up the environment and the tools to build the simplest application - the one that does nothing. By experiencing the steps needed to build such a small binary, you start to grasp how to work with the new technology.
First-hand experience is the most powerful learning tool for the majority of people in the world and we should give it the right priority.