Best quote about software ever
The late John Vlissides once said:
"A hallmark - if not the hallmark - of good object oriented design is that you can modify and extend a system by adding code rather than hacking it." - John Vlissides, The C++ Report, February 1998
He goes on to say: "In short, change is additive, not invasive. Additive change is potentially easier, more localized, less error-prone, and ultimately more maintainable than invasive change."