Yup, all of these. Sometimes I look "around" the problem, like, "I found THIS directory but the file 'z.txt' was not in it!" or "Not only could I not find 'z.t

Yup, all of these. Sometimes I look "around" the problem, like, "I found THIS directory but the file 'z.txt' was not in it!" or "Not only could I not find 'z.txt' I could not find THIS directory it was supposed to be in." Check to see that it is really a file, not a directory. "I found 'z.txt' in THIS directory but it was zero bytes in length!" In terms of "fail early," my larger programs have a section called Pre-Flight Checklist, which looks for files (and that they are files), databases, that the databases have the expected tables and the correct columns, and so on. Are the files sufficiently recent? More or less the expected length? Because this is ETL stuff, it's usually okay to push this stuff up as early as I can.