This claim is both ridiculous and wrong. And the reason for it being wrong was stated concisely by clemburg.

Now you claim to use modules all of the time. This is good. But that most certainly was not your original claim. In fact you said that you like to avoid them and avoid using any modules and scripts you do not personally understand. So do you or do you not use LWP? What about CGI? Do you understand them? I know that figuring out how they really worked took me quite a while. (I don't claim to know them in detail.) I would guess that I know more Perl than you do. But I freely admit to never having learned the internal implementation of DBI. Should I? What priority should I give that?

In order to live and be a productive person in a complex society, you need to use stuff you don't understand and have to take on faith. That is life. And there is no magic barrier saying that you can realistically get away with doing so everywhere except Perl scripts and Perl modules. Nope. There is no wall there. There are enough good scripts and modules that I would be stupid to not be willing to use them. But mistakes get made. (Even in my stuff.) So I try to stick with tested stuff which has good bug reports. I make heavy use of the local research agency. In short I perform my due diligence...

The world is full of uncertainties. Those uncertainties regularly destroy lives both figuratively and literally. Of such is life made. You don't have a choice, so learn to deal.