Welcome to the illustrated version of davorg's post, where we explore the reason Perl was written the way it was written using examples.

What if you wanted to do "'" using single quotes? ''' won't work, so the slash was introduced: '\''.

Now, what if you wanted to do "\\'" using single quotes? '\'' won't work -- we know from the previous paragraph that it would give a lone single quote -- so we need to escape the slash: '\\''. But that still doesn't work because the quote is not escaped. We escape the quote as well: '\\\''

In single quotes, when the slash isn't followed by another slash or by a single quote, Perl doesn't require you to double it.