I want some large-scale study about the impact of APIs and lower-level abstractions and how those impact the user-facing features built on top of them. Files (as in this post by @957492b3) are a great example, but ease of error reporting/error messages is something I see all the time—if you tell the user "operation failed" what you really mean is that it was too hard to report a good reason (or you just don't care).

https://jenson.org/files/ 

 @367fbbb9 Well said