For me, it was the argument passing syntax. I had to look up the magic sigil for doing hashref stuff every single time.
One day I tried Python, learned that everything is passed by object reference, and set Perl aside and never looked back. There was so much less mental overhead that Perl never lured me back.
There was an experimental auto-deref feature since Perl 5.14
And it's already gone again since 5.24.
That's because it didn't work reliably. There were at least a couple of situations where Perl would have had to guess which operation you were trying to perform, so the feature was a source of potential bugs.
Hi. I really liked your book
Modern Perl.
Yes unfortunately auto-deref had problems.