How much error handling should you build in? For example, I have a very simple program that takes one sort of ID and converts it to another in about 15 separate stages. Should I build in error handling at each stage (similar to below) or only at the places where it's highly likely to fail after bad data? 

else {
    print STDERR;
die ("Unable to proceed.  ID may be invalid.  Exiting.\n");

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(Initial input and the first calculations at the main concern - after that, there's almost no chance of error.)

I don't want to overdo it, same as I don't want to overcomment, but I also don't want to leave later maintainers wondering why it wasn't set up properly to start with!

In reply to Error handling by Ari

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