The program-design version of the law of diminishing returns. The 80/20 rule says that roughly 80% of the problem can be solved with 20% of the effort that it would take to solve the whole problem. For example, parsing e-mail addresses in "From:" lines in e-mail messages is notoriously difficult if you follow the RFC 2822 specification. However, about 60% of actual "From:" lines are in the format "From: Their Name ", with a far more constrained idea of what can be in "user" or "host" than in RFC 2822. Another 25% just add double-quotes around "Their Name". Matching just those two patterns would thus cover 85% of "From:" lines, with a tiny portion of the code required to fully implement RFC2822. (Adding support for "From: user@host" and "From: user@host (Their Name) " brings coverage to almost 100%, leaving only really baroque things that RFC-2822 permits, like "From: Pete(A wonderful ) chap) KISS Principle (2003-11-17)
