Spent about an hour debugging a bit of code today.  I was attempting to read data from a particular source and kept getting back failure codes.  After some debugging I discovered the data didn't actually exist in the source I was reading from. 

This put me back to investigating where I wrote the data out.  Restarted the scenario and verified that I actually called the data writing API and that it succeeded. 

Now what?  Well the data clearly wasn't there so I concluded the data writing must be failing in some odd way.  I eventually found the data writing code and was horrified to find the following definition.

HRESULT WriteSomeData(...) {
  // We don't support data of this type
  return S_OK;
}

Personally I thought this warranted an error code (perhaps E_NOTIMPL).  But given the situation I must conclude the author successfully failed to write the data.