Software Maintenance

Maintenance is the activity of modifying a software product after delivery to correct defects, improve performance, adapt to a new environment, or prevent future problems. Despite being treated as a "lesser" activity, it typically consumes 40–80% of total software lifecycle cost and is where most software professionals spend most of their careers. The dominant failure mode in maintenance is not technical: it is modifying code without first understanding it.

Three ideas drive everything below: