Comment by msluyter

A third problem is that, depending on the project, one's recollection might be pretty fuzzy. A fourth is that, while you might be a great programmer, perhaps you've never had the opportunity to do the work of the design or greenfield development, meaning, you may not have a ton of insight into the design work that went into the project. E.g., perhaps you mostly do maintenance work on a large number of projects, so your overall knowledge of each is fairly shallow.