Professional developers are so certain of their code and tests that they are maddeningly casual about making random, opportunistic changes. They'll change the name of a class, on a whim. They'll notice a long-ish method while reading through a module and repartition it as a matter of course. They'll transform a switch statement into polymorphic deployment, or collapse an inheritance hierarchy into a chain-of-command. In short, they treat software the way a sculptor treats clay—they continuously shape and mold it.