It depends on how the programmer learns. There is no one learning method. I for example learn by reading, doing, fixing, reading, doing fixing. I have learnt more recently than ever by having more code to maintain. Before coding was writing functional one offs. Lately I have had to update my code and extend functionality. And that has made me better just because coming back to a 1 year old code, you learn the need to document and write readable code not just functional code. I think having to use other people's code or maintain the code of others would have the same affect. I am not a great coder and will always be learning. Who knows maybe as I get to different levels of understanding my learning methods will change also.