Of the four project development variables - scope, cost, time and quality - quality isn't really a free variable. The only possible values are "excellent" and "insanely excellent", depending on whether lives are at stake.
Kent BeckHow good the design is doesn't matter near as much as whether the design is getting better or worse. If it is getting better, day by day, I can live with it forever. If it is getting worse, I will die.
Kent BeckResponsible Development shares many practices with XP but the roots are different. Responsible Development's values are honesty, transparency, accountability and responsibility. These lead me to pairing, test-first, incremental design, continuous integration and so on because they support the values.
Kent Beck