He means that if you are going to parse an XML file, use an XML module from CPAN because it already handles all the funky cases you will end up needing to handle and that if you want to reinvent the wheel (re-code and debug all the parts already done in a module) then you'll have to learn some new skills because IRS isn't going to cut it. ;)

You mentioned wanting to be a good programmer before using modules, in Perl, using modules is a big part of being a good programmer.