So much great information has already been shared. Charlotte is right on target about the causes and characteristics of burnout: "Often, at the root of burnout are factors related to the organization, agency, and/or profession (e.g., low wages, confusing policies, no support)."
While the others (VT, STS and CF) are specific to caring/helping professions, burn-out can happen in any setting the characteristics (Charlotte mentioned above) are present from office managers to car salespeople.
Harry