What's the most important thing to learn in the Perl world?

ghenry has asked for the wisdom of the Perl Monks concerning the following question:

Is it hashes, references, objects or something else?

Update:

After reading the replies, I realise that my question was not enough. What I really wanted to ask was:

What's the most useful thing to learn after covering everything in Learning Perl?

Or is it a case of learn something when it becomes apparent and always use perldoc?

Thanks,

Gavin.

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