Damn right. Info for the OP and any other newbie struggling with this: when you do

use WWW::Mechanize;
[download]

Perl will internally translate this to a request to look in @INC for a subdirectory 'WWW' containing a text file 'Mechanize.pm'.

So @INC should contain a list of roots of library trees, not a list of directories where the actual module source files are in — except when the module name is a top level name, i.e. it doesn't contain any "::" (or "'").