There is a mix. Some things you can learn from the code other things you need documentation. Often it's the domain knowledge that is hard to glean from the cod

There is a mix. Some things you can learn from the code other things you need documentation. Often it's the domain knowledge that is hard to glean from the code. Especially when bug fixing. For example: The domain expert told me this output was wrong but the code appears to be doing exactly what it claims to. Trying to get a domain expert to set down and explain why the output is wrong is a skill that took me way to long to develop. Now sitting down with a pen and paper running through the logic with an expert is one of my most treasured information gathering techniques.