One of the early foundational principles of Perl was "TMTOWTDI" (http://wiki.c2.com/?ThereIsMoreThanOneWayToDoIt for the unfamiliar). The intention behind this was cool: do "it" whichever way makes the most sense for your particular situation.
But the end result was horrible: everyone did "it" every possible way, and that, IMO, is the underlying reason for Perl's reputation for being unreadable.
I also think it had a great deal of impact on the development of later languages and principles, which tend to focus much more on removing freedom from the programmer and enforcing idiomatic ways of doing "it". Today, you're far more likely to encounter modern code written by different programmers which looks very similar -- at least on a line-by-line basis, anyway. At the architectural level, it's still a big game of Calvinball.
But the end result was horrible: everyone did "it" every possible way, and that, IMO, is the underlying reason for Perl's reputation for being unreadable.
I also think it had a great deal of impact on the development of later languages and principles, which tend to focus much more on removing freedom from the programmer and enforcing idiomatic ways of doing "it". Today, you're far more likely to encounter modern code written by different programmers which looks very similar -- at least on a line-by-line basis, anyway. At the architectural level, it's still a big game of Calvinball.