Dan Drezner makes some nice points in response to the Forbes article that lists academia as one of the least stressful occupations. While he rightly notes that adjuncts face a great deal of career stress, he concedes that those of us in tenure or tenure-track positions enjoy a degree of autonomy and flexibility that those in careers at similar pay levels do not have.
Similarly, with teaching, many of us endeavor to improve our teaching or offer new courses because we believe it's important to do so. Taking on such a commitment invariably generates new stresses -- teaching a new course sometimes leads to initially lower course evaluations, generating a new course is harder than repeating an old one -- and we could usually just not do these things and still keep our jobs. Nonetheless, we take on the task of improving our course offerings, and the concomitant stress, because to quote Hyman Roth, "this is the work we have chosen," and we think this is the best way to do it.